so chapter 10 is moving us to removing microorganisms from within the body so we're going to talk about antimicrobial treatment if you remember chapter nine was all about uh limiting our exposure to microorganisms by decreasing the number of organisms that are in our environment so this begins with a little bit of History uh the medical revolution in the 1930s with Alexander Fleming's discovery of penicillin as a usable antibiotic and the mass production of antibiotics to make them available to the general public uh antibiotics themselves are common metabolic products of most aerobic bacteria and fungi in other words we are extracting chemical components from existing microorganisms and using them to inhibit the growth of other microorganisms uh basically these are chemicals that are produced as microbial antagonists uh remember we talked a lot about how uh in microbial antagonism organisms will fight for their space fight for their area uh within the body that they are using as their normal habitat okay now antimicrobial drugs have greatly reduced the incidence of certain infections but they haven't gotten rid of infectious disease altogether and they probably never will the reality is that most organisms will eventually find a way around antibiotic now we are dangerously close to a postantibiotic era a lot of textbooks say this the reality is that in 2014 the World Health Organization sent out a memo saying the postantibiotic era is here we have a lot of drugs that do not work against certain types of microorganisms so expect in the next few decades to see a lot of resistant infections uh sort of creeping up in numbers now the overall goal of antimicrobial therapy is to destroy the infective agent without doing any harm to the host we're going to refer to this as selective toxicity organisms that are selectively toxic or I'm sorry drugs that are selectively toxic Target the difference between ourselves in other words the host and the microorganism so keep in mind big differences between procaryotes and UK carats as we move through this now your characteristics of an ideal antimicrobial look a lot like the characteristics of an ideal disinfectant or sterilant um again selectively toxic uh non-toxic to host cells so it works on the microorganism but not on us um our preferences for this to be microbic rather than microbic static in other words it kills as opposed to inhibiting U A lot of these actually have to do with maintaining appropriate amounts of the antibiotic within your system for an extended period of time um so functions even when highly diluted bodily fluids or isn't broken down or excreted uh prematurely uh organisms cannot become resistant to it that would be great uh complimenting the host defenses again remaining active in tissues and bodily fluids so it's not broken down or deactivated in some way uh gets to where you need it uh so it's readily delivered to the site of an infection cost always comes in somewhere uh and doesn't disrupt the host Health uh by causing allergies or predisposing you to other infections now these sound very similar to a lot of the characteristics of an ideal disinfectant uh the reality is just like the ideal disinfectant this one doesn't exist because if it did it would work on everything it would kill bacteria never harm us and it would be reasonably priced we'd all have access to it uh so we sort of do the best we can with what we have right now now a little bit of terminology just you need to make sure you're familiar with a chemotherapeutic drug do not be fooled by this it is not specific to any type of cancer treatment chemotherapeutic agents are any chemical used to treat or relieve uh symptoms of a disease or disorder uh chemicals that are used prophylactically are used preventatively basically before you get sick uh we give prophylactic antibiotics to surgery patients sometimes just to make sure that they don't get an infection uh antimicrobial chemotherapy is specific to controlling infection uh antibiotic again those natural metabolic pro products of some microorganisms that are used to inhibit the growth of other microorganisms uh the reality is a lot of the antibiotics on the market are not strict natural products U most of them have been chemically Modified by drug companies making them semisynthetic drugs there are a few out there and I'll mention them specifically uh when we get to them I'll help you make note of them that are what we consider synthetic drug drugs that are produced entirely within a lab in other words chemical reactions were used to produce this drug it has no natural source uh most importantly we see here narrow spectrum and broad spectrum antibiotics uh your narrow Spectrum or limited Spectrum antibiotics will work on a limited number of microorganisms uh in other words if it only works on the gram negative organisms it would be narrow Spectrum uh broadspectrum antibiotics are effective against several different types of organisms uh they're also known as extended Spectrum you can use them on gram positives gram negatives maybe some micro bacterium uh so if it has several types of bacteria that it works on it's considered broad spectrum now if you look at this next slide uh you can see the spectrum of activity for certain drugs uh polymixin uh and how they work make them a very limited Spectrum so narrow spectrum antibiotic uh the one that I feel like you should sort of know is tetracyclin eventually we'll talk about the tetracyclin uh these have the broadest spectrum of activity and the tetracyclin have a very broad spectrum because of how they work if you look they're working on gr negatives gr positives Chamas retsas so four of the five different types of or groups of bacteria that are listed here uh the penicillins relatively broad the Kap penum also broad uh isonas it definitely very narrow uh sort of limited to the MCO bacterium now before you begin antimicrobial therapy there are three things that we like to know uh the nature of the microorganism this is usually done through collecting specimen you send them off to the clinical microbiology lab and they're analyzed by a technician okay is it gram positive is it gram negative what type of organism is it you know uh susceptibility testing can also be done there so there's our second one uh testing for susceptibility or sometimes it's called sensitivity testing in other words we would like to know which drugs work on this particular organism and then your overall medical condition of the patient right how healthy is this person do they have allergies to the drug we'll go through several of these uh in the upcoming slides now the reality is doctors very frequently will begin some type of antimicrobial therapy on the basis of an educated guest okay uh it's an informed decision we don't send everything for testing uh think about coming into the lab or coming into the doctor's office and having something like strep throat uh chances are your doctor could possibly test you for strep throat a lot of them don't if you show all the normal symptoms uh and then they will prescribe an antibiotic without ever doing any type of susceptibility testing because they know what works uh to cure strep throat nine times out of 10 so let's talk a little bit about susceptibility testing uh first first up here this is what's called the Kirby bow method for susceptibility testing um not particularly difficult you guys could very easily do this uh the bacteria in question so your sample from the patient is taken and swabbed completely across plate so we'll cover the plate and bacteria so we would have sort of what we call a lawn of growth it would grow everywhere right and then uh little filter paper discs are actually laid down on top of the bacteria these are going to be about the size of a pencil eraser and all the filter paper discs are actually labeled uh with what type of antibiotic they have in them and how much antibiotic is there uh you push them into the augur a little bit so that they don't fall off flip your plate and incubate it uh after the plate is incubated and the bacteria had a chance to grow you'll pull the plate out and what you can see is that these areas around the disc are clear okay the clear areas are what we call zones of inhibition now in order to determine if this particular antibiotic will work on this bacteria it's not just oh pick the one with the biggest Zone uh what we do is measure the diameter so all the way across your zone of inhibition and compare it to a set of Standards if you look up here let me change the color so you guys can see this so if you look up here okay you'll see INR flx isin 5 G with a set of numbers um R under 17 mm s 22 mm the R means resistant in other words that particular organism is not susceptible to this drug it will not work on that organism and susceptible at 22 mm that's our goal okay if we want to use INR loxin and actually have it work on this particular organism and and inhibit or kill this particular organism the diameter across the zone of inhibition needs to be 22 millim and if you look here this is 10 25 uh our total length is about 27 millim so yes enrofloxacin would definitely work uh you can see this one here Chlor andol if we go down to the bottom uh has a very sort of limited resistance and susceptibility measure if it's under 21 millimeters the organism is resistant if it's 21 or over the organism is susceptible um this one's been measured for you you can see it here the r uh this particular organism is resistant to Chlor and phol okay so this is how the Kirby bow test is done this is what those lab reports that you would get back uh would look like uh telling you that the organisms were susceptible to certain drugs intermediately susceptible so it was between the resistance and the susceptibility numbers uh for other drugs and susceptible to uh ones that would work so you would choose one of the drugs that the organism was susceptible to in the Kirby bow test okay obviously those resistant organisms okay or obviously those drugs that the organism is resistant to okay uh you would not want to use those particular drugs to help treat your p now another mechanism of doing this is with what we call a tube dilution test uh more sensitive and quantitative than the KB B test itself uh what we see is the antimicrobial so your drug is diluted in seral tubes of broth so we will put you can see it down here so we would have several tubes this one happens to be done in a plate okay but here these are representative of tubes so we would set up several tubes uh put the same amount of bacteria in each tube okay uh you would obviously leave some one tube with no drug and one tube with no bacteria just to use as your positive and negative controls uh and then put varying amounts of drug into each tube incubate them and go back and look for growth basically cloudiness of the tube uh what you find is what we call call the minimum inhibitory concentration this is the smallest concentration of the drug you need to actually inhibit the growth of the organism in other words this is the least amount you could use anything less than this is not going to inhibit growth okay see uh the will say this is grams 2.0 gram works one gram does not 0.5 grams obviously doesn't if two grams works that means four will and eight will and so will 16 okay now the minimum inhibitory concentration so we're saying things like lowest dose or amount you can use uh will come into play uh in calculating what we call the therapeutic index now the therapeutic index is something that okay is calculated by by taking the maximum tolerable dose or what we call the NTD right and dividing it by the minimum inhibitory concentration okay obviously the bigger the number uh the safer the choice because you can choose sort of a target range like you see right here okay somewhere between the toxic dose and the lowest dose you could possibly use that's the goal uh drugs that have a therapeutic index with a very small number uh are a riskier choice you've got to be extremely accurate when calculating dosages here because it's very difficult to get below the toxic number but above the uh minimum inhibitory concentration uh what's considered the sub therapeutic number in other words the dose that will not work so accuracy is going to be very key here that's one of those reasons why they uh harp on you during medcal now all of that being said we know that what happens in the body is not necessarily going to match what happens in the lab so inv vitro activity of a drug uh inv vitro means on glass but what we're really saying is what happens in the lab uh is not necessarily what's correlated with invivo activity or what happens in the body right so what happens in the lab isn't always going to match up with what's going to happen in the body uh we see antimicrobial treatment fail for a variety of reasons uh the drug that was chosen uh can't diffuse down into the body compartment where you need it uh lots of things will not diffuse into joints or make it to the blood rain barrier uh you get resistant microorganisms in the infection that weren't in your original sample so maybe the sample was collected poorly or the organisms have mutated and the resistance is a new uh genetic Advantage for the organisms uh we see antimicrobial antagonism where more than one drug is used and the drugs interact and actually decrease the their effectiveness because of the inter action uh people fail to take the drug as prescribed we see that a lot especially in people doing things like stopping medications before uh they've taken their entire dosage or an infections caused by more than one pathogen uh where we see what we call polymicrobial or mixed infections lots of times uh the symptoms don't necessarily go away or they subside slightly uh and then sort of rebound because the drug works on one of the organisms but not on the other so those patient histories we were talking about uh Physicians have to take careful histories before prescribing the antibiotic these will include uh pre-existing conditions that could possibly influence how well the drug Works things like metabolic conditions uh history of allergy to certain drugs obviously you do not want to give someone drug that they are allergic to uh underlying liver and kidney disease because I'm sure you all remember that no matter what if you put it into your body it has to be filtered out that's where your liver and kidneys are going to come in uh infants the elderly and pregnant women are all going to be special scenarios uh because anybody remember hopefully in your head you are thinking of an answer to this these are all cases where the individuals are automatically imuno compromised uh so extra precautions should be taken uh other drugs again increase increasing the toxicity of a drug that's there or having one drug fail okay uh we see this frequently in people that take antibiotics uh and having things like their birth control fail okay genetic or metabolic abnormalities again how the drug is processed is going to be important we don't want a drug um that affects the body because it's processed poorly sight of infection and root of administration go hand in hand uh because the sight of infection will usually help determine the root of administration um I always tell people that usually don't get an eye drop for a respiratory infection there is a reason for that okay root of administration and sight of infection go hand in hand as always cost will play a role I'm going to stop here for the first lecture okay uh breaking them up into smaller units the next one will specifically cover mechanisms of action of antimicrobials [Music]