so in this chapter we're going to talk about antimicrobial drugs so in order for us to understand about antimicrobial drugs we first need to start by introducing some terms and the first term that we're going to refer to is chemotherapy chemotherapy is the treatment of disease with chemical substances that's a very broad definition think about when you think of chemotherapy what usually comes to mind that we associate with chemotherapy and that is probably the first thing that comes to your mind is cancer treatment right cancer treatment patients will undergo chemotherapy but what you need to realize is that chemotherapy is much more broad than that it's not limited to cancer it's basically the treatment of any disease with a chemical substance so an antibiotic would be a type of chemotherapy what is an antibiotic an antibiotic is an antimicrobial agent usually produced by a bacterium or a fungus and bacteria and fungi produced this as a defense mechanism basically to help inhibit the growth of other competitors in their environment and so what you'll see as many of the antibiotics that we use are actually naturally occurring and they're produced by bacteria and fungi and so that's an antibiotic if you think of antibiotics are antibiotics typically useful against viruses and the answer is no we don't take an antibiotic for the cold or the flu because viruses are different than bacteria and so when we start to talk about the mechanisms of antibiotics you'll start to see why they're not effective against viruses viruses are different in their structure in the way that they reproduce etc and so antibiotics are typically not effective against viruses the next term we need to understand is selective toxicity and selective toxicity is the property of some antimicrobial agents to be toxic to a microorganism and less or non-toxic to the host and so when looking for antibiotics you want to choose a drug that displays selective toxicity because you want it to target some aspect of the microbe without harming the host or without harming our own cells and so throughout the semester we've talked about different examples of selective toxicity but one that we've talked about multiple times would be looking at penicillin penicillin inhibits peptidoglycan it inhibits the cell wall prokaryotic cells like bacteria have cell walls made of peptidoglycan in the most for the most part so if we target peptidoglycan we are inhibiting cell wall synthesis in bacteria but do our cells have cell walls made of peptidoglycan and the answer is no our cells are animal cells they lack a cell wall so penicillin is going to display selective toxicity it's going to inhibit the microbe or harm the microbe without without harming our own cells and so selective toxicity is a very important property when choosing an antibiotic so antibiotics are natural metabolic products of bacteria and fungi and they're produced to inhibit the growth of competing microbes in the same habitat this would be antagonism so again it's their kind of defense mechanism think of it as their immune response except it's not in response to anything it's in particular but it's a chemical that they produce to basically inhibit other bacteria from growing in their habitat the greatest numbers of antibiotics are derived either from bacteria in the genre streptomyces and bacillus or olds in the genre Penicillium and cephalosporin and so if we look at this table you do not need to memorize this table but what you want to look at and see is that if you look here so here are gram positive rods so bacillus subtilis we've worked with this one in lab B subtilis produces bacitracin we have polymyxin and so we are going to talk later about what these drugs do if you look at actin on my CDs notice we have Streptomyces streptomyces is a type of bacteria that is filamentous it grows in these filaments so it's fungi like we have many drugs that are derived from this so and for T sub B which is effective against fungal fungal growth chloramphenicol tetracycline if we come down here we have erythromycin neomycin etc if we look at our fungi some of the antibiotics are produced by fungi and so Penicillium Chrissa genom produces penicillin and you might recall that we talked about Alexander Fleming discovered penicillin completely by accident right he was trying to grow staph aureus and on his plate he ended up with this fuzzy fungi and he noticed that in the area where that fungi was that bacterial growth was inhibited and so we are gonna look at what these drugs do in just a moment so what we're gonna do here is we're going to talk about some desirable characteristic of antimicrobial drugs and so actually what we're gonna do for this is I'm going to open up a discussion and what I'll have you guys do is in the discussion I want you to come up with five things that you think would be desirable for an antimicrobial drug for example I'll give you one the drug is selectively toxic and remember that means that it it's toxic to the microbe without harming the host and so what I want you to do is I want you to come up with five other characteristics that you think would be desirable for an antimicrobial drug if you were the one if you were a scientist who was designing an antimicrobial drugs what would be some considerations in choosing an antimicrobial drug and so you're gonna make a list on canvas on another discussion board and this will be a class participation assignment after the date has closed for this then I will post a list to summarize what you guys talked about and what are some desirable characteristics of antimicrobial drugs and so this this slide will actually be a class paper that will be posted on canvas so when we look at antimicrobial drugs and this is something you guys have talked about in lab and that is broad spectrum and narrow spectrum and so if we call a drug broad-spectrum this is an antibiotic that is effective against a wide variety of organisms both gram-positive and gram-negative so a broad spectrum is an antibiotic that's effective against a wide variety of organisms both gram positive and gram negatives and so an example when we talked about the Kirby Bower an example of a broad spectrum was north lock season and you might recall that when we looked at north lock seasons action that it bacteria all of the six bacteria that we tested they were all sensitive to north lock season so that would be considered a broad spectrum so it targets of a wide variety of organisms now in terms of broad-spectrum right they target a wide variety of organisms you might think well it's best to always have a broad spectrum because if we prescribed a broad spectrum it's gonna target whatever bacteria is causing the infection and we don't need to worry about what finding out which bacteria is causing the infection but what you want to think about is that's not necessarily a good thing choosing a broad spectrum is not always the best course of action yes if a patient has an infection that is likely to be life-threatening imminently meaning they're in danger of dying because there's undergoing sepsis or something along those lines right if you don't have time to figure out the infection then yeah a broad spectrum might be the way to go because if you give the patient a broad spectrum it's going to target whatever bacteria is causing the infection however there is a drawback to using a broad spot and that is that if you think about a broad spectrum they're effective against many types of bacteria is that only harming or is is the drug only effective against the bad bacteria and the answer is no it's not only going to inhibit the organism causing the disease but it also has an effect on normal flora and it's going to inhibit normal flora and so not only are you getting rid of the bad bacteria but you're getting rid of the good bacteria too and so that's why sometimes with a broad spectrum you get some side effects that occur after taking a broad spectrum one side effect might be gastrointestinal distress stomach ache diarrhea etc because the drugs might be affecting you our normal flora in the gut which causes an imbalance and causes GI problems another one if you're female you've probably experienced this at some point in your life if you've ever taken a broad spectrum and that is that by taking a broad spectrum you might end up with a yeast infection and a yeast infection happens because when you take a broad spectrum in the vagina there's yeast and there's bacteria when the bacteria are there they're competing for resources with the east and the yeast are kept in check however if you take a broad spectrum now you're killing off the good bacteria that's in the vagina you're getting rid of the normal flora the yeast is not inhibited by this broad-spectrum antibiotic and so as a result when you get rid of the bacteria and not the yeast the yeast is like woohoo freedom it has resources it has space it has access to food and so the yeast starts to overgrow and that's when you end up with a yeast infection and so those are some drawbacks of a broad spectrum the other drawback for a broad spectrum is what's called a super infection that's this definition on the bottom and a super infection is an infection following a previous infection usually by a microorganism that has become resistant to the antibiotics used earlier so basically you're going to get a secondary infection and so the super infection now the bacteria is resistant to the drug that was used previously and so this is a big problem in terms of antibiotic resistance by improper use of antimicrobial drugs or overuse of antimicrobial drugs many many things have led to an increase in the number of bacteria that are antibiotic resistant and we will talk about these in a later slide and so what you want to realize though is that yes there's a purpose for a broad spectrum if the patient's life is in danger prescribing a broad-spectrum might be the way to go however there are drawbacks because broad-spectrum not only get rid of the bad bacteria but they get rid of the good bacteria too and so that would be a drawback of a broad-spectrum so now let's talk about a narrow spectrum and so a narrow spectrum is an antibiotic that is effective against only specific types of organisms and so an example would be penicillin because it targets peptidoglycan and is effective against gram-positive so penicillin would be considered a narrow spectrum because it inhibits peptidoglycan and if you recall when we talked about the cell wall of gram positive and gram negative remember that grande positive had a very thick layer of peptidoglycan while gram-negative have a much thinner layer so if we inhibit peptidoglycan this drug is going to be more effective against gram-positive and less effective against gram-negative and so that would be an example of a narrow spectrum another example of a narrow spectrum that we looked at in lab would be clindamycin you might recall that clindamycin was very narrow spectrum not only did it just not did it just target grande positive but it was specific against staph aureus it did not target bacillus Megatherium it didn't target other types of bacteria it was only effective against staff aureus and clindamycin as a result is useful it's used in topical acne products it's used as a drug on the skin because staph aureus it's normal habitat or normal flora would be on the skin and so Clini myosin is used for acne because it's targeting staph aureus specifically so in terms of a narrow spectrum right the downside of a narrow spectrum is if you if you don't know what's causing the infection then giving a narrow spectrum might not be the way to go because in that case it might not be targeting what's causing the infection however the plus-side of using a narrow spectrum is that it typically targets the organism that's causing the infection it's more targeted and oftentimes you might get better faster as a result of that narrow spectrum drug because the drug is getting to the bacteria that's causing the infection and it's not being used up by other bacteria that are part of your normal flora and so there are pros and cons for a broad spectrum and a narrow spectrum if given the choice and you have time to figure out what's causing the infection a narrow spectrum would be the way to go but in some instances you don't have a choice and a broad spectrum might be the way to go and so this is just comparing the spectrum of activity so if we look at these drugs put on a laser pointer here and so what you're looking at is the spectrum of activities so we have our mycobacteria here we have our gram-negative bacteria our Grande positive our chlamydia x' and our ric study is notice that for tuberculosis right Mycobacterium think about Mycobacterium Mycobacterium has a unique cell wall composition and that is that it's made of 60% mycolic acid so if we're talking about treating tuberculosis right TB we can use drugs that target mycolic acid and so drugs like isoniazid and others that we're going to talk about are effective against mycobacteria specifically but it's not going to be effective against gram-negative her grande positive because they don't have mycolic acid in their cell wall so that drug would be very narrow spectrum gram-negative right so notice that we have quite a few drugs that might be effective against gram-negative so streptomycin it has some activity against Mycobacterium we have poly mix and we have carpet pens we have tetracycline we have our sulfa drugs our cephalosporins a little bit in terms of penicillin but not as effective and so notice that gram-negative have a lot of drugs that can be chosen some are narrow spectrum so polymyxin is narrow spectrum look at tetracycline though tetracycline is very broad spectrum it targets gram negatives it targets gram positives it targets chlamydia as it targets Ricks ideas penicillin is more narrow spectrum right it targets gram positive specifically it might have a limited amount of effectiveness for gram negatives and maybe a little bit for the chlamydia x' but not very much and so again you don't have to memorize this but it's just to show you that different different antibiotics have different spectrums some are very broad spectrum like tetracycline others like isoniazid is very narrow spectrum it targets a specific group of microorganisms so here is a class paper this one we will talk about together so you don't need to do this on canvas but the question asks you identify at least one reason why it's so difficult to target a pathogenic virus a protozoan a fungus or a Hellmouth without damaging the host cell so you want to think about for each one why is a virus more difficult to target without damaging the host why is a protozoan more difficult why is a fungus difficult why is a helmet difficult and so what I want you to do is I want you to think about this and I want you to pause the video and when you're ready push play and then listen to the answer and so when you're ready pause and then we will go over this together so hope you thought about this let's start with the viruses so this is very relevant to what's going on right now in our life right the corona virus and there are several reasons that viruses are more difficult to treat one is that for viruses they live within host cells right they're obligate intracellular parasites so because they live within a host cell it's more difficult to target the virus without damaging the host cell because viruses are obligate intracellular parasites the other thing about viruses that makes them more difficult to treat would be they are not living they're considered nonliving we can't prescribe drugs that inhibit so all penicillins not going to be effective against a virus because viruses don't have a cell wall viruses are simply a protein coat called a capsid and nucleic acid in the middle in the case of the corona virus the corona virus also has a structure on the outside of the capsid that's called the envelope and the envelope is derived from the host cell membrane meaning that when the virus goes to leave the host cell it takes some of the host membrane with it so as a result because viruses are not living you can't target necessarily protein synthesis they themselves don't have ribosomes to do protein synthesis they use host ribosomes so you would also be targeting the host ribosomes which would give you not selective toxicity right so viruses are not living so we can't target cell walls they don't have them we can't target protein synthesis because they don't synthesize their own proteins right viruses hijack host machinery and as a result right if we were to try and target the things that allow viruses to replicate well that can be problematic because it's using host cell machinery it's using our own cells in order to replicate and so therefore finding drugs antiviral drugs is a lot more complicated than finding antibacterial drugs and so viruses it's more difficult to target because one they live within the host cell so it's more difficult to target those without damaging the host and two viruses are not living so we can't target cell wall synthesis we can't target ribosomes because they don't use their own ribosomes they use our episomes and so viruses get a lot more difficult to treat now if we talk about protozoans protozoans are difficult to treat because they are eukaryotic and animal-like so because protozoans are eukaryotic they're going to have more in common with ourselves then let's say a bacteria so we can't target peptidoglycan they don't have peptidoglycan we can't target 70s ribosomes these cells are eukaryotic they don't use 70s ribosomes we can't target different types of metabolism because their metabolism might be more similar to ours and so protozoans are more difficult to target simply because they are eukaryotic and they have more in common with animal cells and the same then also goes for fungi and that is again their eukaryotic and so because they're eukaryotic there are less differences between fungal cells and ourselves to exploit so finding antifungal drugs is a little more difficult and then lastly helmets you might recall back from chapter 1 that helmets are the parasitic worms right parasitic worms these are eukaryotic and animal cells so these organisms have a lot in common with our own cells because helmets are animals so they don't have a cell wall they're gonna use very similar metabolism that we do etc and so helmets are more difficult to target because one often times they're parasitic they're living within our body and so targeting them specifically can be a challenge but the the big thing about how ments is that because they're eukaryotic and they have they're made of animal cells there are less differences to exploit to find drugs that are selectively toxic and so this is why targeting bacteria often is easier than targeting these different types of other microbes so question for you one disadvantage to using broad-spectrum antibiotics is that de is it red destroy normal microbiota yellow are easily and activated by the host green are extremely toxic blue target host cells and so I want you to pause the video and when you're ready push play and then we will go over the answer so if you said red you are correct a disadvantage to using a broad-spectrum is that they destroy normal microbiota they destroy normal flora they get rid of not only the bad bacteria but the good bacteria too and so that could lead to what's called a super infection yellow are easily inactivated by the host that's not necessarily true being broad or narrow has nothing to do with how they're inactivated by the host green are extremely toxic again that doesn't really have an effect in terms of selective toxicity blue target host cells it doesn't mean that they target host cells it just simply means that they target a wide variety of microbes so now we're going to look at the action of antibiotics and we're going to talk about how different antibiotics work to inhibit microbes from growing so there are a variety of different strategies that antimicrobial drugs can employ to try and inhibit microbes and so there are several ways that these can work one is they might disrupt cell processes or structures of bacteria fungi or protozoans so again it might it might affect the cell wall and if you affect the cell wall well then the cells might die and so disrupt cell processes or structures in the case of viruses viral drugs oftentimes inhibit virus replication so it inhibits the virus from multiplying interferes with the function of enzymes required to synthesize or assemble macromolecules if the organism can't make their macromolecules therefore they can't divide and so we're going to look at some examples of this like targeting DNA replication or targeting protein synthesis destroy structures already formed in the cell so it might be that it it pokes holes in the cell membrane for example so basically it destroys structures that are already formed in the cell and so these are different strategies that antimicrobial drugs can use to try and inhibit microbes so if we talk about drugs being bacterial SCYTL or bacteriostatic again we have talked about this in lab before but if we say that a drug is bacterial SCYTL SCYTL means kill and that means that this drug is going to kill the microbes directly on the flip side if we say that a drug is bacteriostatic static stasis means to stay the same so drugs that are bacteriostatic inhibit microbes from growing it doesn't necessarily kill the microbe it simply stops them from dividing which basically gives the immune system time to catch up and so it just inhibits the microbes from growing and so in some cases choosing a drug that's bacteriostatic might be more beneficial than choosing a drug that's bactericidal and we talked about a group of organisms that we might not want to give a drug that's bactericidal and do you remember what type of bacteria you might not want to prescribe a bactericidal drug and that is we talked about gram-negative bacteria right gram-negative bacteria have an outer membrane and in their outer membrane they have LPS lipopolysaccharide within there they have lipid a if a gram-negative bacteria ruptures if there's a large amount of this gram-negative bacteria and it ruptures and it releases that lipid a lipid a is an end of toxin and it might cause the patient to go into shock and so in that case if the patient has a large gram-negative infection it might be better to treat it with a drug that is bacteriostatic to inhibit the cell from dividing but not caused bacteria to release a lot of lipid a and so again there are pros and cons for each type of drug so this slide is basically looking at the action of antimicrobial drugs looking at the approaches that we have to target bacterial cells so the first one that we have is we have over here inhibition of protein synthesis so inhibiting protein synthesis there are several drugs that are used to inhibit protein synthesis so we have a Zathura myosin or a z-pack what we call a z-pack clinda myosin which we've talked about as you topically for acne tetracycline there's one you've probably heard of so there's a whole group of drugs and they work by inhibiting 70s ribosomes they target 70s some of these drugs target the 50s subunit so the large ribosomal subunit some of the drugs like tetracycline target the small subunit the 30s and so these drugs though collectively are used to inhibit protein synthesis because they target 70s ribosomes now in terms of whether those drugs would be bactericidal or static so if we inhibit protein synthesis you have to think about is it likely going to kill the bacteria or simply inhibit its growth and the answer is that this drug is a static drug it's bacteriostatic it's going to inhibit the microbe from growing because without the ribosome synthesizing proteins the cell is not making enzymes and therefore cannot replicate and so these this class of drugs would be considered bacteriostatic they inhibit the cell from dividing but but they don't necessarily kill the microbe so that's one approach the next approach that we have is going to be inhibition of cell walls so we have several drugs that can that block the synthesis and the repair of the cell wall we have penicillin we have cephalosporin we have vancomycin bacitracin isoniazid we're gonna talk about all of these different types of examples here but basically these disrupt the salt wall now isoniazid is gonna target mycolic acid penicillin is gonna target peptidoglycan and so they have different targets if we think about inhibition of cell wall synthesis would that be Seidel or static and the answer is that this type of inhibition would be Seidel it's going to kill the bacteria because bacteria are rapidly dividing and if they're not able to make their cell wall to kind of grow in size it's going to kill the bacteria so this type of inhibition is actually going to kill the bacteria versus just inhibited it's going to cause the contents of the cell to come out so inhibition of cell walls is going to be SCYTL if we look at the third method which is going to be damage to the cell membrane and so examples of drugs that that damage the cell membrane polymyxin the coolest ins drugs so daptomycin etc these drugs disrupt the cell membrane and so if we disrupt the cell membrane is that going to be Seidel or static and the answer is Seidel it's going to kill the cell because when you disrupt the cell membrane when you get let's say holes in the cell membrane that's gonna cause the bacterial cell to undergo lysis the next mechanism is going to be inhibition of nucleic acids so we'll put here so nucleic acids so meaning that these drugs might target DNA replication these drugs might target transcription they're inhibiting some function of nucleic acids so in terms of inhibiting DNA replication an example of that would be the quinolones so Noor fluxes in that would be a quinolone because that enzyme or I'm sorry that drug inhibits DNA gyrase which is an enzyme that's used to unwind DNA when bacterial D and when bacterial cells go to replicate so basically it's inhibiting the bacteria from replicating its DNA other drugs like refampin inhibits transcription it inhibits RNA polymerase so that's going to inhibit transcription and so that will block the cell from taking the DNA and producing the mRNA which is then going to inhibit protein synthesis so is this mechanism likely to be seidel or static and the answer is static because it's not it's not disrupting structures that are already in the cell it's preventing the cell from duplicating their DNA for example meaning it's preventing it from dividing to form two new cells so it's simply just inhibiting cell division but it's not necessarily killing the bacteria and so that is the fourth mechanism is inhibition of nucleic acids and lastly the last example is going to be inhibition of metabolism so it's blocking some aspect of metabolism that's unique to prokaryotic cells and so one way one type of metabolism that we can inhibit is to target folic acid now we've talked about this over and over again and that is that folic acid ray is a nutrient that bacteria will produce and bacteria produce it to make nucleic acids and so we talked about this when we talked in lab about the Kirby Bower we talked about this when we talked about competitive inhibition right so if we think of sulfanilamide sulfa drugs that class of drugs remember acts as a competitive inhibitor inhibitor for an enzyme that normally converts PABA to folic acid and so if we block Pavla from forming folic acid if sulfa binds to the enzyme instead if the bacteria can't make their folic acid they also can't synthesize their nucleic acids and therefore they can't divide trimethoprim remember is synergistic with sulfanilamide because it targets two different steps in the synthesis of folic acid and so those two drugs both are used to inhibit folic acid synthesis so along those lines would you would you predict that that drug these drugs are static or SCYTL and the answer is static just like inhibiting nucleic acids is static it inhibits the cell from dividing it's not necessarily going to kill the cell so the cell is not able to synthesize bollock acid they can't make their nucleic acids and therefore they can't divide so this class of drugs would be static so the next class paper is again to get you thinking for each of the following actions of antimicrobial drugs explain why each mechanism is selectively toxic or is not selectively toxic so I'm gonna do the first one with you and then I want you to pause the video after I'm done talking about the first one and I want to see if you can think your way through the next four on your own and when you're ready push play to hear the answer so the first one let's talk about the first one so inhibition of cell wall synthesis so is that mechanism selectively toxic or not so is that selectively toxic and the answer is yes that type of drug would be selectively toxic because bacteria have a cell wall and human cells do not so because our cells don't have a cell wall if we inhibit cell wall synthesis that drug is going to be selectively toxic because it's going to target the bacteria with our without harming our own cells so for the next four I want you to think about are there differences let's say for the next one are there differences between the way that bacteria synthesize proteins and the way that we do is there differences in the cell membrane are there differences in terms of nucleic acid synthesis are there differences in terms of inhibition of synthesis of essential metabolites so when you're ready pause the video see if you can think these through first and then push play to hear the answer so let's go over this in inhibiting protein synthesis is that selectively toxic the answer is yes bacteria use 70s ribosomes and our cells use eightieth so these drugs are selectively toxic they're gonna target the microbe without harming our own cells however there is a caveat to this and that is where in our cell do we also have 70s ribosomes so where else do you find 70s ribosomes it's not just bacteria but what other structure in ourselves also uses 70's ribosomes and you might recall that the mitochondria use the 70s ribosomes remember that mitochondria have some of their own DNA and they have their own ribosomes for protein synthesis mitochondria have 70s ribosomes and so if the drug is very soluble and it can get into the mitochondria then you might have problems with side effects the drug would not be a selectively toxic anymore because if it's inhibiting protein synthesis in the mitochondria that's problematic and so some of the drugs that are not as routinely used anymore are often because they have side effects that go along with targeting those 70s ribosomes because if the drug gets into the mitochondria and it affects mitochondrial ribosomes well then that's not going to be a selectively toxic anymore and so there is a drawback but we're gonna say overall that yes this is selectively toxic because bacteria use 70s ribosomes and our cells use 80s next we have injury to the plasma membrane is that selectively toxic and as a general rule no because bacterial cells bacterial cell membranes are similar to ours they're both a phospholipid bilayer and so there are less differences to the cell membrane in ourselves and in bacteria and so oftentimes these drugs don't display selective toxicity one of the things that you're gonna see is that oftentimes these drugs are used topically meaning polymyxin is found in triple antibiotic ointment neosporin it's used on the skin and the reason that it's safe to use on skin is that your skin right the cells of your skin your epidermis are dead so if you damage the cell membrane well those cells on the outside of your skin are already dead so those drugs are more often used topically on the skin versus internally because these drugs don't have as much selective toxicity meaning they could damage host cell membranes as well next we have let me change my ink next we have inhibiting nucleic acid synthesis so is that selectively toxic and the answer is yes this is selectively toxic because bacteria have circular chromosomes oops circular chromosomes and we have linear chromosomes so bacteria have circular chromosomes and we have linear chromosomes so in the last slide when we talked about inhibiting nucleic acids I mentioned that you can target a enzyme called DNA gyrase and that is unique to prokaryotic cells because it's used to unwind circular DNA we don't have circular DNA no harm done right so the this class of drugs would be considered selectively toxic then we get to our last one which is inhibiting the synthesis of essential metabolites and is that selectively toxic yes bacteria synthesize folic acid but we get it from our diet so if we take sulfa drugs or trimethoprim those are going to inhibit folic acid synthesis but it's not going to affect us because we don't use enzymes to convert PABA to folic acid we simply obtain folic acid from our diet and so those drugs would be selectively toxic so now we're going to look at some specific examples of the different mechanisms that antibiotics use to target microbes and so the first mechanism that we're going to look at in more detail are going to be drugs that fall under the category of being inhibitors of cell wall synthesis and so an example of a drug that inhibits cell wall synthesis would be penicillin and penicillin contains a beta lactam ring and the beta-lactam ring is responsible for its action needed so need it to make peptidoglycan and so what I mean by that is that in order for penicillin to inhibit cell wall synthesis it must have that beta-lactam ring being in tact and one of the things that you're gonna see is if that beta-lactam ring is broken for example there are enzymes that bacteria that can produce that make them resistant to penicillin and one of the ways that they do so is by cutting the beta-lactam ring so in order for penicillin to be effective it must have its beta-lactam ring intact so it's the beta-lactam ring that's responsible for the action of penicillin the types of penicillins are differentiated by the chemical side chains that are attached to the rings and so what makes these different organisms are these different drugs target different organisms is depending dependent on these side chains and you'll see this in a minute the way that these drugs work is that they prevent the cross-linking of peptidoglycan and so if they if they inhibit the cross-linking of peptidoglycan that's going to interfere with cell wall construction and you can see in the picture on the right you could see that this bacterial cell that's been treated with penicillin the penicillin has weakened the cell wall and it's caused the bacteria to lyse in terms of our penicillins what which class of bacteria would you estimate that this target more and that is it's going to target gram-positive more and some gram-negative and remember that that's because in gram positive bacteria they have a thick layer of peptidoglycan and so because they have this very thick layer of peptidoglycan that's responsible for the structure of the cell wall if we inhibit that cross-linking of peptidoglycan x' that's going to damage the grande positive cell wall more so when we look at our penicillins we can break them down into several categories depending on if they are naturally-occurring penicillins or if they are partly synthesized and so we'll start with our natural penicillins natural penicillins are extracted from Penicillium cultures and remember that this is a fungi and so if we look at our natural penicillins we have penicillin G which must be injected and penicillin V which is which can be taken orally and so if you look down below and you look at these two drugs right penicillin G versus penicillin v notice that the common nucleus the part that's in purple is what they have in common notice that the yellow box is the beta-lactam ring and then if you look at the side chains on this one of the things that you'll notice is that penicillin V has this extra oxygen and that extra oxygen is enough to make a difference in the way that the drug is administered because again penicillin G has to be injected it can't it's not stable if taken orally whereas penicillin V can be taken orally it can be it can go into the stomach and then be absorbed into the bloodstream and the intestines and then circulate through the body that way and that's an important thing because when you think about drugs administer of the drugs is important because it's much easier for a patient to be able to go home and take an oral medication than to require one that's injected and so just these little small chemical changes make a big difference in how the drug is administered and so these natural penicillins have a very narrow spectrum of activity again they're gonna target gram-positive and so these have a narrow spectrum they target gram-positive specifically and the problem with the natural penicillins though is that they are susceptible to enzymes that are called penicillin aces or more specifically beta-lactam aces and these are gonna see in a minute these penicillin ace or this beta lactamase those are enzymes produced by bacteria that make them resistant so make bacteria resistant to penicillin so if bacteria produce these penicillin ace this enzyme ace tells you enzyme if they produce the penicillin ace they are going to be able to cut the beta-lactam ring and remember that I said that the beta-lactam ring needs to be intact for its activity and so these enzymes that bacteria produce they can cut the beta-lactam ring which basically makes bacteria resistant to penicillin they are no longer inhibited by the penicillin because that beta-lactam ring is not intact for the penicillin to have its effect and so one of the problems with natural penicillin is that these types of penicillins are very susceptible to penicillin ace and also its narrow activity so if we look at our penicillin ace again this is an enzyme produced by bacteria that allow bacteria to be resistant to penicillin and again it's because it breaks the beta-lactam ring these enzymes are produced by many bacteria but most notably Staphylococcus species and penicillin aces are also again called beta lactamase because of their ability to break the beta-lactam ring and so again what you're going to see is if you look at how penicillin ace works it's going to break that beta-lactam ring and it's going to produce this penicillin oak acid which is not active to inhibit peptidoglycan it no longer is going to be effective to inhibit peptidoglycan and so again this is what makes bacteria be resistant to penicillin so next we're gonna look at our semi synthetic penicillins and so semi synthetic is just like the name suggests it's partly derived from mold and partly synthesized and so that's why it's called semi synthetic it has a part of it that is naturally occurring and the other part has been chemically modified and when they chemically modify it they add or they adjust these side chains if you compare that to penicillin G or penicillin V you'll notice that the common nucleus the part in purple is similar but the chemical side chains are going to be different and what that does is it makes these drugs resistant to penicillin aces meaning that if bacteria are resistant to penicillin by producing penicillin aces you could still prescribe this drug to the patient and these drugs would be resistant to the action of the penicillin II so even if bacteria is resistant to penicillin they wouldn't necessarily be resistant to these drugs because they have chemical modifications so that's one advantage right so one advantage is that it makes them resistant to penicillin aces keeps racing or extends the spectrum of activity because remember that for natural penicillins they're very narrow spectrum they target gram-positive specifically but when you take these penicillins and you modify the side chains it now can allow the drug to have an extended spectrum of activity so not only is it going to target gram positive but if you look at ampicillin for example ampicillin because of its unique chemical sidechains has an extended spectrum it can target many gram negatives as well oxacillin is still narrow spectrum it only targets gram positives but its advantage is that that group of side chains are resistant to penicillin ease again so even if bacteria is resistant to penicillin it doesn't mean they're going to be resistant to the oxacillin and so this is our semi synthetic penicillins so this is just kind of summarizing drugs that are penicillin based and how they've been modified to make them more effective so we have our penicillin ace resistant penicillins methicillin oxacillin these two drugs specifically are much more resistant to penicillin ace than the natural penicillins some of the penicillins again have an extended spectrum that means that they're effective against gram negatives as well as grande positives and so these are our amino penicillins so ampicillin amoxicillin amoxicillin is one they commonly use for kids when kids have infections it's a commonly used antibiotic penicillin plus beta lactamase inhibitors and so for these drugs when they contain the beta lactamase with them the beta lactamase is going to act synergistically now you might recall that in lab we talked about drug synergy that is that two drugs combined are more effective than either drug alone and so when you give a patient a penicillin with the beta-lactamase inhibitor that's going to increase its effectiveness because bacteria now are not going to be able to be resistant to the penicillin because the beta-lactamase inhibitor is going to inhibit that penicillin ace so an example of this contains clove onic acid and clove onic acid is a non-competitive inhibitor of penicillin ace remember what that means when we talk about a non-competitive inhibitor it binds somewhere other than the active site so it binds to penicillin ACE somewhere other than the active site it causes penicillin ace to change its structure and now penicillin ace is no longer able to cut that beta-lactam ring and it's no longer able to inactivate the penicillin and so a drug that is penicillin based with the clove onic acid one that you may have heard of or taken at some point is called augmentin it's a combination drug it's two drugs together and they display synergy because you have a penicillin based drug and the inhibitor of penicillin ace now in addition to having penicillin with the beta-lactam ring we also have cephalosporins and the cephalosporins are also derived from a fungi so produced by cephalosporin sungai so just like penicillin is derived from Penicillium fungus cephalosporin is produced by cephalosporin fungus and notice that it has a beta lactam ring and so the actions of cephalosporins are very similar to that of penicillin in that they both contain this beta lactam right and so because they contain this beta-lactam ring both of these are going to inhibit cell wall synthesis now in terms of drugs that are cephalosporins if you've ever taken like catholics or suffers all those would be examples of cephalosporin based antibiotics in addition to our penicillin based cell wall synthesis inhibitors we also have polypeptide antibiotics meaning that their protein derived and these will also inhibit cell wall synthesis so an example of this would be bacitracin and bacitracin has a narrow spectrum it's a topical antibiotic used for skin infections in post surgical wipes for example it's used to kill gram positives on our skin like staph aureus or certain streptococcus species and so again it's very narrow spectrum it's going to inhibit cell wall synthesis it's also found in neosporin so if you've ever used neosporin on a wound the triple antibiotic ointment one of the drugs that's in that triple antibiotic ointment neosporin is bacitracin if you've ever seen the movie big hero 6 you've probably seen the part where he talks about how he is resist or how he is allergic to bacitracin so that's what they're talking about is this type of antibiotic vancomycin vancomycin is narrow spectrum it used to be used as a last line drug for mersa so Marissa stands for methicillin-resistant Staph aureus when a patient had this methicillin-resistant Staph aureus one of the first things are one of the last resorts would be to give them binkham isin however now it's a first line drug meaning if a patient has MRSA they will often go to vancomycin and so vancomycin is important against mersa now the reason that vancomycin is not used readily meaning it's not like the first go-to drug for any infection is that vancomycin tends to have a lot of toxicity especially in the liver and sometimes in the kidneys and so when patients are prescribed vancomycin it might be that it's administered in the hospital or if they do get to take it home the patient might have to do liver screening to make sure to check for liver enzymes and making sure that the drug is not having a negative effect on the liver the other problem is is now we're also starting to see the evolution of vancomycin resistant or vancomycin intermediate staph aureus meaning that now staph aureus is starting to gain some resistance to vancomycin and so that's a very scary thought what used to be our last line drug for MRSA now bacteria are starting to evolve to have some resistance against vancomycin as well and so we'll talk about antibiotic resistance at the end of this lecture so next we're going to look at our anti Michel bacterial antibiotics and so for these these are drugs that are gonna are gonna target mycolic acid remember that for Mycobacterium they have mycolic acid 60% mycolic acid in their cell wall and so to target those types of bacteria is a different approach and so one drug that is anti mycobacterial would be ice in iodine and it is used because it inhibits mycolic acid synthesis in actively growing cells and this is used in combination with other anti TB drugs and TB remember is referring to tuberculosis and so isoniazid is a drug used for TV because Mycobacterium tuberculosis has mycolic acid in its cell wall and so this would be a drug that is used to inhibit the mycolic acid another example would be a drug called ethane butyl and FM butyl is going to inhibit the incorporation of mycolic acid and so it's a relatively weak anti TB drug and it's usually used as a secondary drug to avoid resistance problems so again it's usually going to be used in combination with other anti TB drugs just to help with avoid resistance problems so you might have a patient that is taking drugs for TB and they might have a cocktail of a combination of drugs to try and target tuberculosis which is again remember hard to treat because that waxy mycolic acid is difficult to target and so these are some drugs that are also inhibitors of cell wall but they're not targeting peptidoglycan now they're targeting mycolic acid specifically and as a result these drugs again are going to be narrow spectrum and they're narrow spectrum because they're not going to target gram-positive they're not going to target gram-negative they're used specifically for Mycobacterium so these drugs would also be considered narrow-spectrum so the next mechanism of action is for inhibition of protein synthesis and so remember that for this class of molecules for this class of drugs these drugs are considered selectively toxic because these drugs target 70s ribosomes remember that prokaryotic cells use 70s ribosomes ourselves use 80s ribosomes and so there are several drugs that are used to inhibit protein synthesis one drug would be chloramphenicol chloramphenicol is going to bind to the 50s portion of the ribosome and it inhibits the formation of the peptide bond so it inhibits the peptide bond between forming between the amino acids tetracyclines tetracyclines will interfere with the attachment of tRNA to the mRNA ribosome complex so it will inhibit the tRNA from coming in and binding streptomycin is going to change the shape of the 30 s portion and it causes the codon the mRNA to be read incorrectly and so it's going to inhibit bacterial protein synthesis now again remember that these drugs are considered to be selectively toxic because they inhibit prokaryotic cells without having as much of an effect on eukaryotic cells the exception to that is going to be if they happen to get into the mitochondria right because within that organelle if these drugs are very soluble and get into the mitochondria it can inhibit protein synthesis in the mitochondria as well and so you don't have to memorize all of these drugs and their action but I wanted to kind of give you an idea of what types of drugs that you might have heard of would fall in this category of inhibiting protein synthesis so chloramphenicol its broad-spectrum its inexpensive but it's highly toxic and affects the formation of blood cells and so chloramphenicol is not used as often anymore because of its toxicity and so it's not it's not used as often we have clindamycin clindamycin however is narrow spectrum it's used for acne and you might remember when we did our Kirby Bower test in lab that clindamycin targeted staph aureus specifically it did not have an effect on any of the other five bacteria that we're tested but it was effective against staff aureus and so as a result clindamycin is used topically for acne it's narrow spectrum and it's useful on the skin for acne we have our amino glycosides an example of this would be streptomycin it's toxic and can cause auditory damage meaning it causes problems with hearing and as a result it's not used as often because of that reason we have our tetracyclines tetracyclines our broad-spectrum they're useful because they can penetrate tissues making them valuable against tricks Etios and chlamydia z' which are harder to target but the problem is is because they're broad-spectrum they can suppress normal intestinal microbiota and so as a result you might get side-effects remember we talked about the downside of using broad spectrums right that if you not only target bad bacteria but good bacteria that that can cause either a super infection or cause GI symptoms gastrointestinal systems because of an imbalance of the intestinal mic Beata and so tetracyclines or doxycycline those are drugs that were used for acne but again there are some drawbacks to using those we have our macrolides so our macrolides would be erythromycin ASA through myosin cliff through myosin ASA through Meissen you've probably heard of as a z-pack if you've ever taken a z-pak that's aids a through Meissen one of the one of the benefits of a z-pak or ASA through myosin is that where a lot of times for drugs especially like let's say it was amoxicillin it might be a 10-day course of antibiotics three times a day so 30 pills that a patient has to remember but for ASA through myosin the course of treatment is much shorter so you take two pills initially and then one pill for a several days after that and then you're done it's a lot less number of pills for patients to remember and therefore can be better for patients who are more likely to forget to take their medication and we'll talk about later that forgetting to take your medication or not completing a course of treatment for an antibiotic is not a good thing because when you do that that's what leads to antibiotic resistance and so Aiza through myosin has been used often for it's an alternative to penicillin and it's used often to treat streptococcal and staphylococcal infections so to treat ear skin and respiratory type infections and so a lot of times if you have respiratory symptoms the doctor might prescribe you a z-pack the problem is is by overusing z packs now the Azoth her Meissen we're starting to see a lot more resistance to azo through myosin as a result because of its overuse anytime you overuse or over prescribe a medication the more likely bacteria are going to become resistant to it and so these would be--you're macrolides the next class of drugs that we're going to talk about are going to be our nucleic acid synthesis inhibitors and so these are going to inhibit mRNA or DNA replication and so an example of this would be rep myosin and RIF myosin is used to inhibit mRNA synthesis and so because it inhibits mRNA synthesis that is going to block the bacteria from making proteins ro myosin is useful because it's able to penetrate tissues it does a really good job of getting into tissues that are generally difficult to penetrate so it's used for example it can reach therapeutic levels in cerebral spinal fluids and abscesses because of its ability to penetrate tissues it also then makes it useful for TB so it has anti tubercular activity it's able to be used against TB so put used for TB because TB in that condition the Mycobacterium gets into the lungs and you get scar tissue that builds up and it gets walled off but the roof of myosin does a good job of penetrating tissues and makes it useful for TV it's limited in a spectrum because it can't pass through the cell envelope of many gram-negative bacteria so it's not very broad spectrum it has a more narrow spectrum because it can't get through the porins for example in the gram-negative bacteria one of the side effects of verbum Ison is the appearance of orangish red urine feces saliva sweat and tears and so that can be a side effect that can be a little startling to patients who are taking this and it causes this red orange appearance in various body tissues or body fluids rather the next group that falls under our nucleic acid synthesis inhibitors would be our quinolones and our fluoroquinolones examples of this now dick-suck acid this is synthetic and it's used to inhibit DNA gyrase now DNA gyrase is an enzyme used unwind DNA for replication because remember that prokaryotic DNA is circular eukaryotic DNA is linear so bacteria have this enzyme this unique enzyme this DNA gyrase to unwind circular DNA we don't have this enzyme because our chromosomes are linear and so this is why these drugs are selective are selectively toxic nor phlox's in and ciprofloxacin which we call cipro they have broad-spectrum relatively non-toxic now that is a little bit debatable if you've ever taken any of the phlox's ins which fall into the quinolones you may see a warning when you take those medications and that is that they have a warning on them that they may cause tendon ruptures it could be while you're taking the drug it could be years down the line after you finish take these drugs so while oftentimes they're written as being relatively non-toxic they do have some potential for toxicity and so again a lot of these fluxes ins have a warning about an increased risk for tendon ruptures I can tell you myself I have taken moxifloxacin which is a velox and I had some very odd side effects from taking that drug I was hallucinating I couldn't sleep I had tachycardia I had all kinds of really odd symptoms as a result of taking that drug and once I looked into it when I had these side effects I found that online other people reported these same side effects and so it actually probably is more common than we know and so they were I was prescribed the a velox for a sinus infection and a later doctor said that was completely unnecessary like that was like hitting an ant with a hammer using something very strong for an infection that didn't actually need that and so while the the slide says they're relatively non-toxic know that there is some toxicity associated with these fluxes and type drugs fluxes ins are used often for urinary tract infections so UTIs and for anthrax so cipro specifically is commonly used but there are other drugs in that family of drugs that are used for the same purpose next we have injury to the plasma membrane and so remember that for this mechanism of action these drugs are not necessarily selectively toxic and that's because eukaryotic and prokaryotic cell membranes have a lot in common it's much more difficult to target something specifically however these drugs can affect the synthesis of bacterial plasma membranes so it blocks fatty acid synthesis we have lipopeptide antibiotics of daptomycin this is produced by streptomyces which is a bacteria and it's used for skin infections it attacks the bacterial cell membrane and it's active against gram-positive polymyxin B is also topical so it's used on the skin it is bactericidal it kills bacteria because when you damage the cell membrane it puts holes in the membrane which kills them but polymyxin B is effective against many gram negatives as well and so polymyxin B is again one of the other antibiotics it's combined with bacitracin and neomycin in non-prescription pointment so again in triple antibiotic ointment neosporin polymyxin B is going to be in there to target the gram-negative bacteria as well again many of these drugs that inhibit the cell membrane these drugs are going to be used more likely topically on the skin because your outer layer of skin your epidermis is dead and so if you happen to inhibit the cell membrane on your skin cells those cells are already dead so not going to be as toxic to you as it would be to take these drugs internally however there are some uses for this there also used to treat drug-resistant Pseudomonas aeruginosa and severe urinary tract infections so polymyxin B can be taken internally but typically it's reserved for if you have particularly drug-resistant infections so again Pseudomonas infections or a severe UTI then polymyxin might be taken orally and then the last class is going to be inhibition of metabolic pathways so inhibiting the synthesis of some sort of metabolism so what we have here is we have our sulfanilamide or sulfa drugs and remember that our sulfa drugs will inhibit folic acid synthesis and bacteria make their own folic acid and that allows them to synthesize their nucleic acids it allows them to make their nucleotides and so if bacteria can't make folic acid they can't make their nucleic acids and then they can't make their proteins as a result remember that the way that sulfanilamide works is that it's a competitive inhibitor for the enzyme that PABA normally binds to so pappas normally the substrate and it binds to this enzyme and it creates folic acid sulfanilamide is a competitive inhibitor it binds to that enzyme and it prevents PABA from binding and if PABA can't bind the bacterial cell can't make that folic acid precursor they can't make folic acid they can't synthesize nucleic acids and so these drugs work by inhibiting metabolism they block bacteria from making folic acid and so when they block bacteria from making folic acid the bacteria can't synthesize their nucleic acids and so these drugs are going to be bacteriostatic they're going to inhibit bacterial growth again what makes these selectively toxic is that for humans we don't make folic acid we take in folic acid from our diet but bacteria are going to synthesize it so these drugs can be selectively toxic remember that sulfanilamide and trimethoprim are sulfa drugs are an example of drug synergy and they work together for synergism because they target two different steps in the pathway to block folic acid and so when you combine the two they are much more effective than either drug alone only 10% of the combined concentration is needed when compared to the drugs used separately so you can give the patient a much much lower dose by combining those two then if you were to give them either drug alone this this combination this trimethoprim and sulfamethoxazole this is used for urinary tract infections under the trade name bactrim so if you've ever taken back drum for a UTI that's what it is it's this combination drug of sulfa drug with trimethoprim and they work by inhibiting bacteria from synthesizing folic acid and so this is just showing you how these two drugs displace energy so here is our sulfamethoxazole here our sulfa drug and here is our trimethoprim here so what this is showing you is paba is normally the substrate so the normal pathway is the yellow so PABA normally binds to an enzyme and PABA gets converted to dye hydrophilic acid then there's another step where the dye hydrophilic acid gets converted to tetrahydrofolate acid and then the Tetra hydrophilic acid is used to make the nucleic acids it's used to make DNA and RNA and so what happens is is that the sulfa drugs are competitive inhibitors and they block the step from paba to dye hydrophilic acid because it's blocking the enzyme that would normally bind to paba trimethoprim works by inhibiting not that step but a different step it is going to inhibit the transition from the dihydrofolate acid to the tetrahydrofolate acid and so it's blocking its own unique step so by combining these two drugs it's more likely to shut down this pathway entirely because if if one is not being as effective the other one is inhibiting it at a later step and so that's why these two drugs displace energy because they're working together to target the same pathway but in a slightly different manner a different step within the pathway and so this is an example of drug synergy and so this is looking at this example if you were to look at it on let's say a Kirby Bower plate so on the Left we have a disc that has the antibiotic amoxicillin and club club onic acid so again remember that the clove onic acid is the inhibitor of penicillin ace and we have another drug on the right now what you can see is the dotted lines that are here show what the clear zone should be right so if you look across this way that's your zone of inhibition and so what that means is that if you also extrapolate and you go this way the clearing should end where this dotted line is but notice you have this additional clearing in between that's the synergy the two drugs combined are more effective than either drug alone if we look at our example when we did our Kerby power here is your example of drug synergy we have our trimethoprim and our sulfa drug side by side and so notice that you would expect for this one the clear zone would probably end somewhere around there this one the clear zone might end right about there with the dotted line is but yet we have this enhanced zone of inhibition between these two drugs because those two drugs display synergy they are more effective combined than either drug alone so question for you penicillin works by inhibiting blank synthesis so how what is the mechanism of action for penicillin does it work by inhibiting protein synthesis red cell wall synthesis yellow plasma membrane synthesis green or nucleic acid synthesis blue so you can pause the video think about your answer and then when you're ready go ahead and push play so if you said cell wall synthesis you are correct so penicillin works because it prevents the cross-linking of peptidoglycan and so as a result bacterial cell walls get weak and it causes lysis to the bacteria as a result so penicillin is a cell wall inhibitor so again this slide is just summarizing the five modes of antimicrobial drugs that we've talked about and for each one it gives you some examples now when you're studying this you don't necessarily have to study every single drug that I put in this in the slides what you want to focus on is use your study guide that it gave you to guide you before what drugs are important to know so I'm very specific in what drugs I'm asking about specifically and if there's a question that's related to the five modes of antimicrobial drugs you might not you don't need to say all of the drugs that are on the slide but you should be able to give me one example of that type of drug so for example inhibition of cell wall synthesis right so an inhibition of cell wall synthesis the example drugs for this penicillin cephalosporin bacitracin vancomycin those are all different examples of an Eben's of cell wall synthesis they have different methods of action right bacitracin is an amino based a protein based type of antibiotic penicillin is derived from fungus cephalosporin is derived from fungus etc so these would be different examples of inhibitors of cell wall synthesis mechanism number two inhibition of protein synthesis so that is going to block proteins from being synthesized because it's going to target 70s for episomes targets 70s ribosomes and so we have chloramphenicol erythromycin tetracycline streptomycin etc Aiza through myosin right these are all examples of inhibitors of protein synthesis when you're studying this you also want to know and review whether the drugs are bacteriostatic or SCYTL so go back and review that as well this for this category inhibition of protein synthesis again selectively toxic because it targets 70s ribosomes humans have 80s ribosomes so just like cell wall synthesis selectively toxic because bacteria have cell walls human cells don't mechanism number 3 inhibition of nucleic acid replication and transcription so either they're going to block DNA replication or they're gonna block transcription and so examples of this would be our quinolones so like ciprofloxacin for example refampin etc these drugs would have selective toxicity because bacteria have to replicate circular DNA for example and they use different enzymes than than we mechanism number four injury to the cell membrane an example of that would be polymyxin B again that's the one that's in triple antibiotic ointment neosporin it's used topically this category of drug is not necessarily selectively toxic and again because human cell membranes are very similar to bacterial cell membranes and then our last one is going to be our inhibition of synthesis of essential metabolites so looking at sulfanilamide and trimethoprim right these drugs are going to inhibit the formation of folic acid they're going to inhibit the formation of folic acid and so bacteria make folic acid so this drug would be selectively toxic it will target bacteria without harming the host so here is our class paper again we're going to go over the answer so after you after I read the question go ahead and pause the video and think about your answer and then when you're ready then go ahead and play this and get the answer so what is the most common mechanism that a bacterium uses to resist the effect of penicillin and so again pause this think about your answer and when you're ready come back and and listen to the answer and so the answer is that bacteria produce penicillin ace which not with sorry which cut the beta-lactam ring and inactivates penicillin so the most common way that bacteria resist the effect of penicillin is that they produce this penicillin ace they make this enzyme which cuts the beta-lactam ring on penicillin and it inactivates penicillins action and so that is going to make bacteria resistant to penicillin and again at the end of this lecture we're going to focus on what are the other ways that bacteria become resistant to antibiotics because you probably know that antibiotic resistance has become a major problem so next we're going to talk about how we treat bacteria in biofilms bacteria and biofilms behave differently when they are free-living and so bacteria that are in biofilms are often unaffected by anti microbials bacteria and biofilms remember are about a thousand times more resistant to antimicrobial drugs than bacteria that are not in biofilms and so antibiotics often cannot penetrate the sticky extracellular material that surrounds the biofilm so again if they have a difficult time getting through that glycocalyx and bacteria and biofilms also express a different phenotype and have different antibiotic susceptibility profiles than free living bacteria so there are several treatment strategies when trying to deal with biofilms one way would be to interrupt quorum sensing because remember that quorum sensing is the signaling pathway that bacteria use to attract a bacteria to the biofilm and so if we can disrupt the quorum sensing that helps inhibit the formation of the biofilm and so daptomycin has shown some success with this mechanism also adding dnace to antibiotics aids in the penetration through the extracellular debris and so again it's gonna help breakdown that biofilm which helps get the drugs to where the bacteria is impregnating devices with antibiotics prior to implantation and so this would be a prophylactic way to prevent a biofilm from forming some antibiotics though aminoglycosides actually caused biofilms to form at a higher rate than they normally would and so we have to be careful with which antibiotics we prescribe so next we're gonna look at tests to guide chemotherapy before actual antimicrobial therapy can begin three factors must be known to help guide the treatment and so the first is going to be the identity of the microorganism causing the infection because again if we look at the spectrum of activity penicillin is very narrow spectrum it targets gram-positive specifically and so without knowing the organism that's causing the infection if you were to prescribe penicillin and that patient has a gram-negative infection that drug is not going to be effective against that drug it's not going to be effective against that infection and so knowing what organism is causing the infection is important to help guide appropriate antibiotic therapy and so again we don't want to just prescribe a broad-spectrum just because it's gonna kill everything because there are side effects and there are drawbacks for using a broad spectrum and so it's helpful to know the identity of the microbe causing the infection also the degree of the microorganism susceptibility or sensitivity to various drugs because let's say we are treating a patient who has a urinary tract infection and let's say we get a urine sample from this patient and we take that urine sample and we swab it on a curvy bar plane and we do an antibiotic sensitivity test well you have to think that even if we know that the UTI is caused by E coli 90% of UTIs are equal why even though that's the most common bacteria that's going to cause the infection that still doesn't necessarily tell you how that particular bacteria is going to respond to the antibiotics because we have different strains of bacteria and they have varying levels of antibiotic sensitivities meaning they have varying levels of resistance so while some ecoli might be susceptible to bactrim for example or cipro that doesn't mean all ecoli would respond and so it's good to know the culture and sensitivity test the Kerby Bauer test to know how that microbe responds to various drugs and then lastly you also need to consider the overall medical condition of the patient because different drugs have different toxicities like remember vancomycin has liver toxicity so you're not going to give a patient who has a weak liver Bank Meissen it could do more damage than it would be helpful so these are there are a lot of things that come into play before a physician prescribes an antibiotic and all of these vary all of these variables have to be considered before prescribing an antibiotic you can't just prescribe any old antibiotic for an infection you need to have some lines as to what drug should be used so identification of the infectious agent should begin as soon as possible it should occur before antimicrobial drugs are given before their numbers are reduced right because once the number of bacteria in the body gets lower it's harder to detect direct examination of biofluids sputum or stool samples is a rapid method for detection right so if we wanted to look at what type of bacteria is causing an infection in the gut well a stool sample would be the way to go or if I wanted to know what type of bacteria is causing the urinary tract infection getting a urine sample would be the way to go and so direct examination of body fluids doctors often begin therapy on the basis of immediate findings and informed guesses and what that means is that they don't always perform a culture and sensitivity test oftentimes they can make assumptions about what is likely causing the infection if it's an upper respiratory type infection it's more likely to be caused by grand positive bacteria so they might choose drugs that would be more common or would target those types of bacteria or if it's a urinary tract infection it's more likely to be gram-negative for example we'll learn in lab why that is but that basically so not always will the doctor do a culture insensitivity sometimes they might begin therapy like for a urinary tract infection they might prescribe a drug right away before the results come back based on what is historically useful against the UTI and then when they get the results back from the urine culture then they might adjust if they find that the drug that they prescribed if the bacteria is to it then they they might switch their course of treatment and say okay now you need to switch to this other antibiotic so but again they often don't want to wait if a patient has a urinary tract infection they're often very uncomfortable and possibly in a lot of pain and so making the patient wait several days to get the results from the urine culture in terms of what antibiotic to use is not always the best course of action and so again doctors sometimes will make informed guesses based on the fact that it is a UTI and they might prescribe a drug that is typically useful but again still get the culture and sensitivity test to determine if that is the appropriate drug epidemiological statistics may be required right and so you really need to make sure to identify what's causing the infection in order to undergo the right type of therapy so the disk diffusion method or the Kerby Bauer again also known as antibiotic sensitivity culture and sensitivity test is used to determine the appropriate antibiotic for treatment the advantages to using the Kerby Bauer method is that they're the most common it's easy it's inexpensive and very little skill is required the test is highly standardized you might recall that when we learned about this in lab right we talked about how this test is standardized and that is that we use that Muller Hinton auger and it's poured to four millimeters in depth to control for lateral diffusion the plates are incubated at 37 degrees because that is like human body temperature the pH of the auger is seven point two to seven point four to mimic the pH of the blood etc so this test is very standardized it's consistent across different labs which makes it an advantage so that the results are fairly easy to interpret what you would do is remember we talked about this in lab right you take whatever sample so again let's say we're doing a urine sample and you would swab the bacteria across the Muller Hinton auger and then you would dispense those antibiotic disks and so if we look at these antibiotic discs right notice that for some of these disks the bacteria grows right up next to the disk would you say then that bacteria are resistant to this drug or are sensitive to this drug and that would be it's resistant right the antibiotic has no clearing no zone of inhibition it's not inhibiting growth so what that tells us is that this bacteria is resistant to whatever this drug is notice that this disk has a very large clear zone it has a large zone of inhibition and so just seeing whether or not it has a zone of inhibition itself is not sufficient to tell you whether it's sensitive or not again you have to compare to that standardized table so just like we did in lab if your zone of inhibition is less than 14 millimeters for example it might be recorded that the bacteria is resistant if your clear zone is let's say between 15 and 17 it might be recorded as being intermediate intermediate means that it's somewhat effective but not completely and I'll come back to that in a minute if the zone of inhibition is let's say 18 millimeters are higher then we would report that as that the bacteria is sensitive to that drug meaning the drug is effective and you get these very large zones of inhibition so you would use this information on these plates you pick an appropriate drug because you would want that that bacteria to be sensitive to your antibiotic now if you have several sensitive drugs then let's say you might pick the one that has a narrow spectrum so that you don't have a lot of side effects right if you are working with a bacteria that is resistant to many drugs so you might recall that when we did our kirby Bauer with Pseudomonas Pseudomonas aeruginosa was resistant to everything except the nor phlox is in the only thing that it responded to with the nor flexes in so let's say you had a plate and for all of your discs the bacteria was resistant except one and let's say that that one drug has some effectiveness and it's recorded as being intermediate it's not resent resistant it's not sensitive it's somewhere in between what that means is if we report that the bacteria has intermediate susceptibility what that means is that we would only prescribe this intermediate susceptible drug if there is no other drug that the bacteria is sensitive to or that there's no other usable drug that the bacteria is sensitive to like if the patient is let's say allergic to penicillin but the bacteria responds to penicillin well that's not going to be all that helpful if the patient can't take it so if there's no sensitive drug the doctor might have to choose to use the drug that the bacteria has intermediate susceptibility but if that drug is the one that's prescribed the intermediate susceptible drug that would require a higher than normal dose so either the length of treatment would need to be extended maybe not a 10-day treatment maybe it's 20-day treatment or if safe the dose itself might need to be increased but if you get bacteria that show an susceptibility well a higher the normal dose would be required to to test this or to be effective and so this is your Kirby Bower and again you guys learned about this in lab now there's another test that's useful for determining an antibiotic and that is what scalding what's called an e test and this is a gradient diffusion method and so the way that this works is there is this plastic strip this absalom etre and it's coated with an increase in concentration gradient of the drug so notice that whatever the units are let's say that this is nanograms per microliter i don't know what the concentration units are but let's say whatever it is so this is 256 this is 192 so notice that the numbers are getting smaller so this number up here is the highest dose of the antibiotic this number down here is the lowest dose of the antibiotic so we have this gradient method right so we have decreasing concentrations of the drug now when we use these strips these gradient strips they give us a little bit more information and that is that this is used to determine what's called the minimum inhibitory concentration m.i.c this is the lowest concentration that can be used that would inhibit or prevent bacterial growth so not only does it tell us just that one concentration so the Kerby Bower is like a yes or a No this will actually tell you what is the lowest concentration that you can use that would inhibit bacterial growth so it gives you an idea of what concentration would be effective to inhibit the bacterial growth and so this is another diffusion method but again it's a gradient diffusion it doesn't just say sensitive or resistant but it actually tells you the lowest concentration again the minimal inhibitory concentration that that drug can be used now in vitro activity of a drug is not always correlated with the in vivo effect meaning that you might do a Kirby Bower test right and antibiotic sensitivity test and you might see that on the dish that the bacteria responds to that antibiotic but that doesn't always mean that that's what happens in the patient and so failure of antimicrobial treatment is due to several things one could be the inability of the drug to diffuse into that body compartment there are certain parts of the body that are difficult to penetrate maybe the drug doesn't get to the brain or the cerebrospinal fluid or the joints or certain abscesses in the skin etc and so it might be that it's difficult to get the drug to where the infection is there may be resistant microbes and the infection that did not make it into the sample collected for testing or it could be that bacteria had in the in the tissue had evolved to be resistant during the course of that testing that you were performing and so what you didn't detect before now bacterias antibiotic resistant which might make the treatment that you use fail an infection is caused by more than one pathogen it's mixed some of which are resistant to the drug so you might pick out the bacteria that's the most prevalent in the infection but there might be other bacteria that are in the infection that you didn't detect initially and that other bacteria might be resistant to the drug or potentially the patient did not take the anti microbials correctly so they didn't finish their antibiotic they didn't take it at the proper spacing meaning they didn't take it three times a day basically the patient did not adhere to the antimicrobial treatment and so as a result the treatment has failed because they didn't finish their course of antibiotics for example so when we talk about drugs we can talk about a drugs what's called therapeutic index and that is the ratio of the dose of the drug that is toxic to humans as compared to its minimum effective or therapeutic dose so basically what dose you can give that's toxic compared to the effective dose the smaller the ratio the greater the potential for toxic drug reactions so if we have a therapeutic index of 1.1 that's a fairly risky choice that's not necessarily a drug you want to prescribe because it's almost as equally toxic to the person as it would be effective so a very low therapeutic index is definitely going to be a riskier choice a therapeutic index of 10 a higher therapeutic index is going to be a safer choice because that means that it's not as toxic as it is effective and so the drug with the highest therapeutic index has the widest margin of safety and so again that's important when you prescribe a drug especially if you're considering the overall health of the patient right you don't if a patient is already immunocompromised or is already in a weakened state giving them some drug that's potentially very toxic it's not gonna be the way to go because that drug could end up doing more harm than good and so the next part is going to be looking at resistant to antimicrobial drugs so this would be a demo that I would normally do in class but I'll walk you through it even though it's not a large-scale demo like we do in class so what we're looking at here is notice over on the right we have these resistant levels and so if you think about bacteria in the body even if you have let's say e coli in the gut not all E coli strains are the same they're going to have varying levels of resistance the green are going to be the low resistance the pink have the high resistance and then there's levels in between so I did this in rainbow order so the green is low the yellow is a little more resistant the orange is a little more resistant and the pink is the most resistant and so before you take an antibiotic right your population your microbiota is a collection of these different types of microbes some have high resistance some have low resistance some are somewhere in between and so the way I actually do this when I demonstrate this in class is I have a plastic bin and it has these balls of different colors so the green balls that are in the bin are super glued to the bin meaning they're hard to take out the ones with the herbs sorry the ones that are pink that have high resistance those are the ones that are going to be tightly stuck to the bin the ones with the low resistance so the green have a very loose adhesive which means it's easy for them to come out so you have your population and so I did this I represented this that we're starting with an equal number of each color so we have three oranges we have three Pink's we have three green three yellow so that's your original population now let's say that you have let's say that you have strep throat right and strep throat is caused by streptococcus pyogenes and it's a bacterial infection and so you go to the doctor and the doctor does hit the throat culture so they swab the back your throat they do the rapid strep test and let's say it comes up as being positive for strep so what's going to happen is that once you so you have your infection and after selection is referring to starting the antibiotic so you start your antibiotic treatment right and so let's say that your doctor prescribes amoxicillin three times a day for ten days so you start taking your antibiotic and let's say you know for three days in four days in you start feeling better right your symptoms resolve your throat stops hurting and you go okay well you know I feel better I don't need to finish my antibiotic my mom and my sister do this constantly and it drives me insane because they will say well I'm gonna save it for the next time that I get sick I'm gonna keep this drug and if I get these symptoms again I'll just take the rest of this later think about what the problem with this is why is it bad to not finish your antibiotic so if you have a population and it has varying levels of resistance some bacteria is very highly resistant some bacteria has very low resistant if you take an antibiotic which bacteria are gonna die first the low resistance or the high answer is the low resistance are gonna die first natural selection by by green ones by by yellow and maybe let's say one yellow happens to stick around right so when you take the antibiotic the weak ones are gonna die first the ones with the least amount of resistance natural selection survival of the fittest right so the bacteria that have the higher resistance are going to survive initially and so if you start your antibiotic and you don't finish it you've killed off the weaker ones first but you didn't finish your course of treatment so you didn't get rid of everything because remember your Kirby Bower is assuming it's a certain dose meaning the drug will be effective over a normal course of treatment if you don't finish that drug you're not going to kill everything the stronger ones are going to survive and so what happens is is that you after selection you end up with a new population we have three pink ones still we have three orange still and we have one yellow still so after selection notice how my population has changed right all the greens are gone most of the yellows are gone so the ones that were easier if I was the antibiotic so again imagine I have my demo with my clear box and the different balls in it if I'm not looking and I reach in and I grab those bacteria the the little balls if I go to grab them out it's gonna be easier to grab the ones that are loosely stuck to the box right the ones that have the weakest adhesive on them so if I'm randomly I'm the antibiotic and I'm not looking great I'm just reaching in and I'm grabbing out the ball I'm gonna pull out I'm gonna kill off the weaker ones first the ones that are less likely adhered to the box so the green ones die off some of the yellow and stay off and so notice that my population looks different now I've gotten rid of its competition I've gotten rid of its good bacteria and so what happens is is that after selection those are going to go to reproduce so now you end up you have two yellows because each yellow the one yellow were reproduced I'm going to end up each of the Reds reproduce and each of the orange reproduce and so look at the distribution of my final population relative to my initial population so if I look at my final population notice I have a lot more antibiotic resistant bacteria in that population I have now shifted the frequency of the antibiotic resistant bacteria and so I have basically helped the bacteria because by only taking the drug for a short period of time I got rid of the weaker bacteria for them and basically now they have better access to resources food space etc and the ones that are resistant are going to survive and reproduce and so this is why there this is how drug resistance can happen is that if you don't take your antibiotics properly right or you're taking your oh if doctors are over prescribing drugs right you're gonna end up with a scenario like this so several key points though when you're thinking about the evolution of drug resistance the first one is that the antibiotics do not create the resistance allele it's not because I prescribed penicillin that bacteria think about it and make a conscious effort to make a protein that makes them resistant to penicillin that's not how this works so the antibiotic does not create the resistant allele the variation in resistant resistance was already in the population I already had tyria that we're resistant or during this stimulation the bacteria acquired the ability to become resistant but it's already present in the population the antibiotic does not cause the resistance what the antibiotic does though is the presence of the antibiotic cause the resistance allele frequency to shift whereas before the pink ones we only had you know three out of 12 now we have one two three four five six out of 14 so almost half of my population now is highly antibiotic resistant so the antibiotics itself doesn't cause the resistance so it's not like we should stop using antibiotics that's not the point the point is is that it's misuse of the antibiotic or overuse of the antibiotic that is leading to antibiotic resistance because those bacteria are already in the population and it's if we use the antibiotic right and it's not used appropriately that is going to help select for bacteria that are antibiotic resistance and so now we see a shift in the population and now most of the bacteria this present is now resistant to that drug and so that is kind of an overview as to how antibiotic resistance evolves and so there are four main mechanisms for bacterial antibiotic resistance meaning ways that bacteria have evolved to make them less sensitive to a particular antibiotic and the first mechanism for this is going to be reduced permeability and what this means is basically that in this case the antibiotic is less likely to get in and this happens through several mechanisms it could be that you get decreased expressions of these porns and remember that porins are found in gram-negative bacteria in their outer membrane and it might be that possibly the bacteria start or stop I should say producing the porns at such a high level and because of the lack of porins the antibiotics are less likely to get in another possibility for reduced permeability is that there could be a physical change in the porn protein to reduce the permeability meaning that they get a mutation in the porn that makes the antibiotic less likely to get in and lastly this could be a change to the cell wall structure and that can happen because maybe the bacteria acquire the ability to produce capsules or slimes and remember that capsules and slimes help to protect the bacteria against antimicrobial control mechanisms the second mechanism for antibiotic resistance is restricted access of antibiotics meaning that in this case although the antibiotic might get in there are these efj luxe pumps and these a flux pumps are basically these pumps and this is the bacteria's way of pumping the antibiotic back out of the cell meaning the antibiotic gets in but now it's going to pump it back out think of it it's kind of like it's a bouncer at a club it's gonna push it back out and say you can't come in here the third type of mechanisms for antibiotic resistance are altered targets of the antibiotic and so here we go and in this case this prevents the antibiotic from binding to the target molecule caused by the mutation and this can be seen for almost every antibiotic class an example of this is remember that we talked about that bacteria have an enzyme that converts paba so folic acid and remember that sulfanilamide or the sulfa class of antibiotics act as competitive inhibitors to PABA for the actors competitive inhibitors for the enzyme that converts paba to folic acid and so in this case the enzyme itself might get a mutation so that sulfanilamide can no longer bind and no longer inhibits folic acid synthesis and so that's what we mean by we say antibiotic target site alteration so that enzyme changes that's the target site and because of that sulfanilamide no longer binds and it's no longer able to prevent the bacteria from producing folic acid the last one is going to be antibiotic inactivation and this can occur either through the degradation of the antibiotic meaning that they might actually break down the antibiotic or potentially the antibiotic becomes modified and this prevent this modification might prevent the antibiotic from binding to its target for example bacteria like Staphylococcus for example remember can produce beta lactam aces or more specifically penicillin aces and that those enzymes are able to inactivate beta-lactam antibiotics meaning that they cut that beta-lactam ring and that no longer allows the penicillins or the cephalosporins from being able to inhibit cell wall synthesis and so now we're going to look at how do bacteria come to be antibiotic resistance like how do they gain the ability to do these various things so let's look at how bacteria acquire the ability to become antibiotic resistant and the first is what we call vertical gene transfer and that occurs during reproduction between generations meaning going from one generation to the next and so in humans and plants this happens going from parents to their offspring in bacteria remember that bacteria don't reproduce sexually instead they reproduce asexually which simply means that they just make a copy of themselves and they do that through DNA replication meaning that they're gonna make an exact copy of their DNA to produce two daughter cells however the enzyme responsible for this is DNA polymerase and DNA polymerase is not perfect DNA polymerase during replication can make mistakes and if it makes a mistake it's called a mutation and so a mutation can be a way that through vertical trans vertical gene transfer meaning again we're going from parent to offspring and that mutation might make it so that they acquire the ability to be antibiotic resistant for example this could lead to a mutated porin remember in the last slide porns can become mutated and make it less likely for the antibiotic to get in this can also lead to altered antibiotic target sites so again like the example when we talked about PABA being used to make folic acid it might be that you get a mutation in that enzyme that no longer makes sulfanilamide able to inhibit folic acid synthesis and so this would be a considered vertical gene transfer the next one is what we call horizontal gene transfer and this is the transfer of genes within the same generation and so there are three main types of horizontal gene transfer that we will look at the first is going to be transformation the second will be transduction and the third is going to be conjugation and in the next slide we'll talk more specifically about this now in order for there to be horizontal gene transfer again it's within the same generation and this is basically a way that bacteria can transfer antibiotic resistance genes from one cell to another and these are typically going to be transferred on what we call plasmids and you learned in lab that plasmids are extra chromosomal DNA sequences and when we get to chapter eight we'll talk more about what are called transposons which are these jumping genes and that these can be passed from one organism to another and because of these resistance genes being able to be transferred this can lead to what we typically call superbugs which are bacteria that are resistant to a large number of antibiotics they might be resistant to only one if they're not a super bug or in some cases some bacteria are resistant to many many many types of antibiotics and those would be the ones that we would refer to as these superbugs so now we're gonna talk briefly about the three types of horizontal gene transfer and we will talk more about the specifics of this when we get to chapter eight and so the first mechanism for how bacteria acquire the genes necessary for antibiotic resistance is through what we call transformation and this is when naked DNA is transferred from a dead donor into the competent recipient and so if we look here we have our dead donor cell and when this donor cell dies it lyse is open and it might release some of its genetic information and so if you look here notice so here are these DNA sequences and one of these might be an antibiotic resistance gene remember in lab when we looked at transformation we treated the recipient cells with calcium chloride that neutralized the charges on the DNA and that allowed the bacteria to take up those DNA sequences it wasn't from a living cell it was from DNA that was simply outside the cell and the DNA went in and if it incorporated into the recipient cell now the recipient cell has acquired the ability to become antibiotic resistant the next mechanism is something called transduction and transduction uses a virus and specifically what we call a bacteriophage which is just another name for a type of virus that infects bacteria and the phage acts as a genetic vector passing DNA from the donor to the recipient and if that donor DNA incorporates into the recipient that then allows the recipient cell to become antibiotic resistant remember in lab when we set up a plaque assay we use the t4 phage and the t4 phage infected the e.coli now during this process it's totally possible for the bacteria to pick up some of the donor DNA before the virus causes the bacteria to lyse so if you notice here is this phage infected donor cell and it's possible that during phage replication and production of new phage that it might incorporate that antibiotic resistance gene into the phage genome and then when that donor cell lysis and it released the phage and the phage go on to infect a new cell now when they inject their DNA into the recipient cell to make this cell be a virus producing factory it's possible that this antibiotic resistance gene incorporates into the recipient cell chromosome and now that makes this recipient cell also able to antibiotic-resistant and the last mechanism is what we call conjugation and conjugation is going to be the transfer of genetic material from one cell to another involving cell cell contact so notice in the first two mechanisms it's not that the cells come in contact and the first one the cell takes up DNA from the outside the second mechanism it was through a phage the phage acted as a vector the third one though when we talk about our conjugation now we're getting cell-cell contact and so in gram-negative bacteria there are plasmids that carry genes that code for the formation of sex pill a and remember that sex pill i our projections from the donor cell that contacts a recipient and helps to bring the two cells into direct contact and so during conjugation when we get this plasmid this plasmid allows the bacteria to produce the sex pee and then during replication of this plasmid it might transfer some of that plasmid into the recipient cell and now the recipient cell has the antibiotic resistance gene and it might also have the gene that allows this recipient cell to produce sex pili as well and keep passing on genetic information most of you have probably heard about MRSA in the news before chem MRSA stands for methicillin-resistant staphylococcus aureus and again we pronounce that MRSA and this essentially means that this strand of bacteria is resistant to many of the antibiotics that we have to treat this type of infection this is the leading cause of healthcare-associated infections meaning that you acquire this infection while in a healthcare facility being treated for something else according to the Center for Disease Control the CDC in 2011 there were 80,000 460 Fork 461 cases of MRSA reported and in 11,000 285 of those cases resulted in the death of the patient the good news is that MRSA cases are starting to decrease in the health care setting the bad news is that there have been 13 cases of what is called Versa which stands for vancomycin resistant staph aureus since 2002 and vancomycin is generally considered to be a last resort antibiotic for patients because it has high toxicity however some strains of staph aureus are now resistant to our last our last resort antibiotic and that's a scary thought so studies show that about one in three individuals carry staph aureus shown here as these grape-like clusters in their nose and on their skin usually without illness about two in 100 individuals carry MRSA and MRSA is typically spread from person to person on contaminated hands skin or objects in the community most Merson factions are skin infections like the one shown in the picture and it starts out as a small and small red area and it might turn into a painful red swollen or to the test touch abscess that fills the pus in a matter of days one of the ways that doctors can determine if the abscess is caused by staph aureus is to swab the wound and then grow it on mannitol salt agar like we did in lab the special plate the MSA augur is formulated to grow staph aureus taken from the skin if you see growth on an MSA plate and it turns the augers yellow then it's probably staph aureus because staff is Osmo tolerant meaning it can grow on high salt and it can ferment the mannitol to produce acids which causes the phenol red to turn yellow and so you guys got to test yourself to see if in fact you carry staph aureus as part of your normal flora now that's to tell you if staph aureus is present if we want to look at if the bacteria is antibiotic resistant like to be MRSA the wound is swapped and then an antibiotic sensitivity tests will be performed like we did in the lab remember we did our Kirby Bower test if the bacteria grows right up next to the antibiotic disks so as you can see here as the bacteria grew right up to the death disk that tells us that the bacteria is resistant to the antibiotic meaning that the antibiotic had no effect on the bacterial growth at all however if there's no growth around the antibiotic disk then we would say that the bacteria is sensitive to the antibiotic and so notice here notice we have this clearing around the disk which means that in this case this antibiotic on this disk inhibited bacterial growth notice that if we look at the plate for MRSA there's only one antibiotic that the that the MRSA is sensitive to so notice here and that is the vancomycin now notice that the growth on the plate is gold color and it's golden color is where the species name comes from member aureus a you because a you is the Atomics atomic symbol for cold now although in the community mrsa only causes typically a skin infection in medical facilities mercer can cause life-threatening bloodstream infections or sepsis it can cause pneumonia necrotizing fasciitis which is flesh-eating disease as well as surgical site infections and so in this case Marissa can be actually quite dangerous so this is a question to get you guys thinking in addition to not finishing a cycle of antibiotics or taking it as prescribed what else can society do to minimize the creation of new antibiotic resistant bacteria and so remember we did the example in class about how when you don't finish an antibiotic like let's say you were prescribed a 10-day dose if you only take that antibiotic for let's say three days well then now you're killing off the weaker bacteria first and allowing the stronger bacteria to survive and you end up with a population that is more antibiotic resistant than the initial population and so we want to think about what else can society do to try and minimize the creation of new antibiotic resistant bacteria and so I want you to just go ahead and pause the video and think about your answers and then we will go ahead and talk about what these ways are so when you're ready go ahead and push play so the first one that we will talk about is that one of the ways that we can prevent antibiotic resistant infections would be to prevent the infection in the first place and so how do we prevent the infection in the first place well this can occur through hand-washing proper food preparation meaning to follow proper food safety immunizations if if possible and so if we don't get those infections then they're not likely to become antibiotic resistant bacteria the second way that we can prevent this is to prevent the spread of the infection and so again like in a healthcare setting taking proper precautions to try and prevent the spread of that infection from one patient to another and so that would be one way that we can help to minimize the creation of new antibiotic resistant a third way is to track infections and what that means is that the CDC or the Center for Disease Control begins to track these infections to learn how they spread the risk factors for contracting the disease etc again to better study how to prevent the spread like how do we prevent passing this from one patient to another and that then allows us to take proper precautions the next one is to improve antibiotic ad station and stewardship and what that means is basically this would be to help basically get doctors to not prescribe an antibiotic that is not needed let's say for example a patient has a cold remember that the cold is caused by a virus antibiotics are not effective against a virus and so in some cases patients will go to the doctor because they're not feeling well and they might demand that the doctor give them an antibiotics so that they can feel better and in some cases it might be that the it might be that the doctor feels this pressure and just to get the patient to stop they might actually prescribe an antibiotic when they know that it's not effective and so it would be important to basically help to get the word out to physicians to really be careful with the way that they prescribe antibiotics that antibiotic should only be prescribed when necessary meaning that the patient has a bacterial infection and so basically improving the way that antibiotics are administered last the next one is going to be to stop using antibiotics in livestock and so in some cases farmers have been giving livestock like cattle for example antibiotics and the antibiotics help to protect them against bacterial infections and it might actually allow the animal to become bigger in size in some cases which produces more meat and so a lot of times farmers will give preventative antibiotics to livestock to basically help with this now the problem with this is again the more often you give the antibiotics to these animals you also might lead to more antibiotic resistant bacteria and then the last one would be develop oops develop new antibiotics and tests so that we have more antibiotics that can be used in cases where our bacteria become resistant to all the current antibiotics that we have so question for you if one measures a large zone of inhibition in the distaff youjin test one can assume that the bacteria are red sensitive to the antibiotic yellow resistant to the antibiotic green unaffected by the antibiotic or blue are producing the antibiotic so go ahead and pause think about your answer and then come back and turn on the video so if you said red that the bacteria are sensitive to the antibiotic that is true if you see that large zone of inhibition remember that means that there's a big clearing around that disk and if there's big clearing that would tell you that the bacteria is sensitive meaning that the antibiotic is effective to inhibiting the bacterias growth and so that concludes our video so when we talk about antibiotic resistant bacteria among the most antibiotic resistant bacteria there are what we call escaped pathogens this is a mnemonic device so the escaped pathogens include Enterococcus faecium Staphylococcus aureus Klebsiella pneumoniae I sent an acid and Oh back der boom Ani Pseudomonas aeruginosa and enterobacter species these groups of organisms cause the majority of hospital-acquired infections with a higher mortality of patients meaning these are the bacteria that are most likely to be antibiotic resistant and to have a high mortality rate in patients who acquire this group of antibiotic resistant bacteria so these are very likely to be problematic now if you think about the modern era of antibiotics in the last you know thirty years or last decade the number of new antibiotics has not increased at the same rate meaning that we're not we're not discovering new antibiotics at a very rapid Brees a very rapid rate and so as bacteria are becoming more and more resistant to antibiotics right because again the more often we overuse the antibiotics think of a z-pack the more often we overuse the antibiotic the more likely the bacteria are to become resistant to those antibiotics and so there are other types of strategies that are now being employed to try and inhibit bacterial growth without having the same level that the bacteria can become resistant so basically we're try to take a different approach of targeting bacteria without bacteria becoming resistant to the antibiotics and so one way that is being tested and it's still undergoing trials is to use what are called bacteriophage so what we call bacteriophage therapy and the idea behind this one is that bacteriophage are viruses that target bacteria specifically so these are viruses that infect bacteria and can be used to destroy bacteria and so the idea is because they're not going to target host cells they're not going to target your own cells they're very specific to a particular virus so they're their host the virus might only infect a coli for example or they might only infect staph aureus or whatever type of bacteria the phage infects so this gives you a more specific way to target a particular bacteria without potentially harming the host because the virus won't affect our own cells and so a lot of work is going into looking at these different phage therapies to see if these phage can be used to target bacteria in the body this is also an interesting way that people are also approaching food safety right because one problem with food safety is let's say produce having microbes on them right and so before we give them to people to eat we want to make sure that the food is as clean or as free of bacteria that are pathogenic and so one idea is to treat food products with phage and the phage would then kill the bacteria which would make the food more sanitary to eat so one alternative to antibiotics is to use bacteriophage use viruses to target bacteria the next one is antiquorum sensing drugs so again if we're talking in terms of biofilm biofilms are going to the quorum sensing is used by bacteria to recruit other bacteria to the biofilm and so there are certain drugs that are being used to inhibit that quorum sensing so to inhibit more bacteria from getting to the biofilm we have fecal microbiota transplants so a fecal transplant and you might have heard about these so let's say for example this is something that happens if a patient is undergoing antibiotic treatment for an extended period of time let's say that a patient had some bad infection and they were on a broad-spectrum antibiotic for a longer period of time remember that the problem with giving a broad-spectrum and taking it for a longer period of time is that it's going to not only kill the bacteria that are causing the infection but it also kills the good bacteria especially in the gut the gut gets very affected by this and so what ends up happening is is when you take these broad spectrums and you get rid of the good normal flora bacteria patients can end up with what's called a c diff infection Clostridium difficile the bacteria was already in the gut but when you took the antibiotics c diff right c diff is harder to kill endospores etc c diff is harder to kill other bacteria in the gut are easier so when you take a broad spectrum you're getting rid of the weak bacteria and the stronger bacteria are surviving and so C diff infections are notoriously difficult to treat it's very difficult to get rid of a c diff infection and so one of the things that they're doing now is a fecal transplant so they might take fecal matter from somebody who lives in the same household who might have similar types of normal flora and they're literally going to take that fecal matter and they're going to put it up the colon and put that back into the gut and the idea is to try and replenish that microbiota with good bacteria and these types of fecal transplants have actually been pretty effective in helping with these types of infections and so it's actually a good approach to trying to restore that balance in the gut we have antibody therapy so giving patients antibodies against the pathogen either the pathogen itself or against the toxin so like for for anthrax for example there is a treatment approved where they actually have purified antibodies that they give to the patients and the antibodies basically neutralize the toxin that causes the anthrax and so that's an antibody therapy you're actually probably hearing about this right now as well when you think about the corona virus one of the things that physicians are doing right now to try and help severely sick patients with the corona virus is by using antibody therapy they're trying to identify donors who have had cope in nineteen and if that patient has gotten better right if they're asymptomatic now they've they've resolved their infection then what they're doing is the people that have had it they're getting plasma donations so the plasma is the liquid part of the blood that's where the antibodies are gonna be if somebody's already had Cova 19 and relatively recently they have a high concentration of antibodies in their blood against that corona virus and so what they're doing is they're taking plasma from people who have basically gotten over the corona virus gotten over coven 18 and they're now taking that plasma from those patients those patients are now donors and that plasma is being infused to patients who are just starting the infection of Kovan 19 and the ones that are really sick to try and help fight off the infection and not have to wait for that patients immune system to catch up it's basically giving them a lot edge to help fight the infection faster and so that's an example of an antibody therapy it's taking antibodies from somebody who's already had the disease somebody who's already had kovat 19 and they have a lot of antibodies in their blood and then giving that plasma to another patient who can then utilize those antibodies to fight off their new infection of Koba 19 and so that's another example of an antibody therapy there are drugs that are being used to target biofilms and adherence so either treating catheters with a certain chemical that prevents biofilms from forming or ways to prevent adherence of bacteria to surfaces etc and then the last one is a really interesting one I got to see a talk about this bedell of Vibrio and like organisms what they call bay lows these bay lows are these small predatory bacteria and they target gram-negative bacteria so like phage they're very specific they have a very specific target and these are bacteria that target other bacteria and so they actually penetrate they're highly motile and actually penetrate the the cell envelope of the gram-negative and they start using the food of that gram-negative bacteria and then it causes eventually that gram-negative bacteria to rupture and so the idea is that we can use these other predatory bacteria that don't harm ourselves their target or gram-negative bacteria and use these bail o's this predatory bacteria to help fight off gram-negative bacteria infections that might be in our body and so these are just some new alternatives that are coming in response to antibiotics because as we've been using antibiotics more and more bacteria have continued to evolve to become resistant to the antibiotics and so there are several new approaches that are are being considered of being that as alternatives to antibiotics and so you'll probably see a lot more of these come up during your lifetime and it's something to kind of keep in mind and look for what are some of these other therapies how do they work what is the advantage of these therapy therapies etc so here our debt some additional resources to watch for antibiotic resistance the first link I posted is a video that shows antibiotic resistance in action it's a start a study that was done at Harvard showing that bacteria can rapidly become resistant to an antibiotic over a very short period of time and then the second video is an animation that helps summarize about what causes antibiotic resistance and so use these as a tool to help you study I will also place these videos in canvas for you to watch as well but there are good examples of antibiotic resistance