hi everyone welcome to chapter 11. chapter 11 is our first of two different chapters this week that are going to dive into uh microbial control mechanisms specifically different types of processes or agents that we can use to limit the growth of microorganisms both on inanimate objects or surfaces and also within or on the surface of the human body so chapter 11 gets into some of the physical and chemical as well as some of the mechanical methods for controlling microbial growth we will actually get into the uh antimicrobials specifically in chapter 12 which is coming up next so without further ado as we dive into microbial control it's important to note that these techniques date back for many many years these are not new processes these are techniques that were started on a very elementary or rudimentary basis a long time ago and have been continuously improved upon to get to some of the protection methods that we know of today so things like burning wood to release formaldehyde or the use of herbs perfumes and vinegar as antimicrobial agents when we talk about utilizing a microbial control method it's important to first of all talk about some of the general considerations and as i mentioned to start off our presentation this evening there's three different uh methods that can be used there's the physical the chemical and the mechanical and oftentimes we're looking at decontaminating an area producing microbes either on inanimate or living or an inanimate or non-living object and we are looking at all different types the whole basically the whole spectrum of antimicro microbial cells everything from bacteria all the way out to the prions which are the infectious protein so we're going to get into first talking about an overview of the different techniques we're going to dive into we have the physical agents which include things like heat and we can either have dry heat or waste heat dry heat includes things like incineration uh this is when you're sterilizing your inoculating loop for a microbial transfer on your candle at home uh this is an example of incineration also the dry oven which exposes the microbes to a dry heat would be a sterilization process and we'll talk about sterilization in a moment but sterilization basically implies that all forms of microbial life including viruses and endospores are removed and then we have the moist heat which uses steam under pressure we're going to talk about the autoclave tonight which looks like basically a giant bank vault and it exposes the microbes to a very high level of heat and pressure for a rather long period of time 15 minutes is really the minimum length of time that we would use the moist heat and then we also talk about things like boiling water and pasteurization which are not methods for sterilization these are actually disinfections so it's important to understand that the disinfect and sterilize are two different things sterilization implies that all forms of microbial life are removed disinfection means that we are reducing the number of microbes to meet a health safety guideline we also talk about radiation and we have two forms of radiation we have ionizing radiation which is typically much stronger these are things like x-rays and gamma rays which will achieve sterilization and then the use of ultraviolet light is a non-ionizing form of radiation and this is considered a disinfection when we get into the mechanical methods most times we're talking about filtration and we can most times either filter air we do this with what's called a hepa filter hepa and that's designed to remove or disinfect the air a lot of times we find hepa filters associated with vacuum cleaners or hvac systems in a house or in a you know a commercial building and then if we're going to filter a heat sensitive liquid something that we can't necessarily boil we can use filtration methods membrane filtration methods that way as well and the filtration of liquids is a form of sterilization we also have the chemical agents we have the gases which we'll talk about ethylene oxide uh today and these can either sterilize or disinfect and lastly we can talk about the liquid chemical control agents these are either antiseptics or disinfectants depending on whether they're on living or non-living objects so let's basically break out the terms so a disinfection is when we remove pathogens but we don't remove all forms of microbial life disinfection is not able to remove endospores okay we can we talk about bacillus clostridium and sporosuccina which are able to generate endospores under stress conditions disinfection methods do not achieve this so this would be for instance if you are cleaning your bathroom and you use lysol to clean your sink that's a form of disinfection it's not going to remove all forms of microbial life it's used disinfection is used only on inanimate or non-living objects if we are using something like hydrogen peroxide which is an antiseptic an antiseptic is the same definition as disinfection except antiseptus implies that it's used on animate or living tissues and then lastly sterilization is kind of the the mecca this is what we're striving to get to sterilization means that all forms of microbial life including viruses and endospores are eliminated this is the table from your book and i really like this table because it does a great job at organizing the information from the slides we're going to go into into the physical agents again the heat and the radiation the mechanical methods which is that filtration and then the chemical agents themselves which are the gases we'll talk about ethylene oxide and then also the liquids and what i like is it also gives us those three definitions the disinfection sterilization and antisepsis so this is definitely a great chapter a great slide to help you organize your notes and determine which techniques are either sterilization methods or disinfection methods so if we were to create a spectrum of the resistance that microbes have to these different methods and kind of rank them from highest resistance meaning that they're the toughest to destroy all the way down to the least resistance we're going to see that things like the prions the infectious proteins and the bacterial endospores are the two most difficult forms of microbial life to destroy with typical disinfection and antiseptic methods however as we get down to things like bacterial vegetative cells the actively growing metabolizing cells fungal cells and the viruses the envelope viruses these are some of the least resistant forms meaning that they are the easiest to kill with the majority of these methods that's really important to understand the high resistance microbes all the way down to some of our least resistant forms and again this just gives you some examples this is table 11-1 from your book and it breaks out the relative resistance of things like endospores and the vegetative cells uh to some of these different methods so take a look at this for instance if we're talking about moist heat you only have to get up to about 80 degrees celsius to destroy the active growing form of a bacterial cell however you need to increase that by about 40 degrees to get your endospores to be destroyed by moist heat radiation again take a look at your difference about 3 000 uh radioactive units your sterile sterilizing gas or ethylene oxide is about 500 units and then we also have a chemical compound which is a high level disinfectant uh it falls in the steroid category it's known as glutaraldehyde and it's a what they call a sporocytal liquid sporocital means that it's able to destroy spores so anytime you see this suffix here sighted cyto implies that it kills so if it was bacteriocidal it would destroy bacteria or if it was virus idle it would destroy viruses so out of these different sterilizing methods these are ones that are able to kill endospores but you can see it requires more of them so moist heat x-rays for radiation the ethylene oxide and the glutaraldehyde are all effective sterilization methods but they require higher amounts to destroy those endospores so this is an important slide to make sure that you know for exam purposes so again we mentioned sterilization destroy all microbe forms and we've already broken out and talked about disinfection which is used on inanimate objects and antiseptics which are used on animate surfaces body surfaces wounds or on surgical incisions and we also need to talk about methods that reduce the number of microorganisms so we talk a lot about sanitation and when you sanitize you are doing things like wiping down surfaces countertops or mopping a floor with a cleaner these are cleansing techniques that are designed to basically limit the number of microorganisms against a health standard to reduce the potential for inspection or infection degermination is a technique where we are looking to go through a mechanical means to reduce microbes on a limited surface area such as hand washing anytime we do a washing of the hands or scrubbing of skin that's an example of degermination where we use that soap and water hot water to decrease the microbial load on a living tissue table 11-2 another great table make sure that you're familiar with this says a lot of the different terminology that we have talked about so far and some of the examples that we're going to go into as we dig into these different definitions a little more in this presentation so we need to talk about microbial death and that's really what this is all about this is the end of the name and the end of the game is to get rid of the microbes so we are trying to destroy their reproductive capability we're applying an agent and looking to stop them from being able to reproduce and increase their population size there are a number of factors that are going to influence how well a particular agent is going to cause microbial death this can include obviously the population size the more microbes the harder and the more concentration of agent we're going to need to kill them the nature of the microbes if there is a level of resistance to a particular chemical agent that's going to influence how easily they're destroyed the temperature and the acidity or ph of the environment the concentration obviously 100 percent concentration of a chemical is going to have a greater impact than if we diluted it down with water to say 10 or 15 percent the mode of action different agents are going to impact different parts of the microbial cell whether it's the cell membrane or the proteins if we go after the proteins those are ones that cells ultimately really can't function without so denaturing or coagulating the proteins is going to ultimately result in cellular death and then anytime there is a presence of an organic material such as saliva or blood that is going to interfere with the ability for the microbial agent to work as effectively so this is a table from your text and it basically gives you an overview of different factors such as time the uh you know and and time for sterilization and how well things work in terms of the chemical agent over a long period of time as time increases so how we decrease the population of cells so what are some of the things that we ask when we determine a method of control first of all do we need to sterilize can we reuse the item this is a big one can the item withstand heat pressure even moisture is the method suitable for that particular material will the agent be able to penetrate that material and obviously is it cost and labor efficient to be able to use this method so these are some of the things that we would ask as we begin to think about the most efficient method of control the antimicrobial agents we're going to see in both chapter 11 and chapter 12 these are going to be very similar we can target several different physical portions of the microbial cell these include the cell wall which we are able to go in and lyse or break open and these are things like the obviously the antimicrobial drugs which we'll talk about in our next chapter the detergents and alcohols we can also go after this phospholipid bilayer this cytoplasmic or cell membrane and we can use the detergents which are called surfactants and these detergents or surfactant molecules actually remove the lipids from the cell membrane causing the integrity of this barrier to be destroyed we can target protein and nucleic acid synthesis so if we stop things like the replication or copying of dna transcription is where dna is copied into an rna message translation is where the rna message is converted to a protein code peptide bond formation this is where we would take the amino acids and connect them with a peptide bond to form a larger more complex protein structure so many of the agents that target this particular channel are things like chloramphenicol which is an antimicrobial agent uv radiation and formaldehyde formaldehyde is that chemical we hear a lot in the preservation of uh bodies prior to funerals and then protein function this is a big one proteins have a particular three-dimensional shape to them that allows their active site to execute a function so here's what i want you to think of as an example of protein function when we talk about that three-dimensional shape think about your shoelaces and you go through and you tie your shoelaces and the rabbet goes down the hole and around the tree and you form your knot that's an example of a three-dimensional protein shape when we denature or disrupt that three-dimensional shape that would be like if i took one of the ends of my shoelace and i pull it and i cause that shoe to become untied when the laces are kind of flapping around in the breeze that's an example of a protein that has lost its three-dimensional structure and is now what we call denatured so things like the alcohols the phenols acids and heat all work at destroying protein function again here's the example here's our nicely folded three-dimensional protein with our active site where the substrate binds we expose this to things like heat or acid this nicely shaped protein now becomes unfolded and that active site can no longer intake substrate and execute its function so the vast majority of the control methods that we use are many of the techniques that you see on this slide so heat cold desiccation means to dry or remove the water we talked about the ionizing and non-ionizing radiation and the filtration so we're going to focus for the next few slides on some of these physical methods of control remember we have three basic categories we have the physical methods the mechanical methods and the chemical methods so let's start with going through these five physical methods of control so we're going to start with heat moist heat is more effective than dry heat moist heat uses lower temperatures and a much shorter exposure time and moist heat does two things it denatures and causes the protein shape to be lost and it also causes coagulation of those proteins so this ultimately seizes uh cellular metabolism basically shuts down all of the metabolic processes that occur in a cell if that happens goodbye to the cell the cell is dead dry heat on the other hand is where we use much more high temperatures we are dehydrating and altering protein structure so for instance one of the biggest techniques that we use here is incineration which is this oxidation of the cells that occurs when we incinerate through dry heat so a lot of times when we talk about dry heat we're talking about things like flaming your inoculating loop i'm using an open flame moist heat we mentioned earlier is that autoclave system which we'll get into in a few moments so anytime we're using moist heat the minimum requirements to achieve sterilization for moist heat are 121 degrees celsius for 15 minutes and there's one piece that should be added here that the book did not include and that is pressure so we go through 121 degrees celsius for 15 minutes at 15 pounds of pressure so 121 15 15. that is the minimum uh quantities that you need to have to achieve sterilization using moist heat we mentioned that dry heat takes much much more so minimums are things like 121 degrees or about 600 minutes look at how much more effective moist heat is versus the dry heat we also talk about two measurements we have tdt and tdp tdt is the thermal death time and this is the shortest time to kill all of the microbes in a sample at a particular temperature so for instance if i had some e coli cells and i told you that i had exposed them to about 63 degrees celsius for about 20 minutes time if i increase that to 67 degrees celsius if i go from 63 to 67 i want to pause for a moment and i want you to think about if i go from 63 to 67 will it take more time than 20 minutes or less time than 20 minutes to kill the cell so i'm gonna pause for about five seconds and let you think about that before i give you the answer all right so if you thought it through 63 increased to 67 the thermal death time should be shorter it should take less time to destroy those e coli cells thermal death point on the other hand or tdp is the lowest temperature to kill all microbes in about 10 minutes time so this is kind of the benchmark to determine what's the lowest temperature that i'm going to get rid of and eliminate an entire sample of microbial cells in about 10 minutes time we've also talked about moist heat we mentioned this i told you earlier this thing that looks like a giant bank vault it's basically this chamber that has a seal to it and we expose the microbes to 15 pounds of pressure and we said minimum is 15 minutes at 121 degrees celsius so remember 121 15 15 and the steam actually has to contact the items surface um the item obviously then if it's contacting the surface it cannot be moisture sensitive so we're not going to put things like paper into the system otherwise it will come out all wilted and destroyed and we mentioned that this moist heat again is responsible for two things the denaturing and the coagulation of proteins we can also use non-pressurized steam and this technique is actually referred to as tymbalization it's this kind of intermittent or periodic sterilization and these this is used on items again that can't survive those traditional autoclaving methods so we use free-flowing steam for about 30 minutes or more and we go for a period of about 24 hours and we repeat the cycle over a course of three days and a lot of times we do this using things like lab media or some canned foods so tyndalization and autoclaving are both methods of sterilization the third method of moist heat control is known as boiling water when we boil boiling is not sterilization it is only disinfection and that's where we achieve about 100 degrees celsius for 30 minutes the reason why this has been kicked down a level the disinfection is it does not remove the endospores so anytime we can't get rid of all forms of microbial life it cannot be sterilization so this is a method of disinfection and the last one that we'll talk about here is pasteurization uh one of the techniques discovered and described by louis pasteur the father of modern microbiology this is basically a technique where heat's applied for a very short period of time at a high temperature we call this the flash method so it's about 72 degrees celsius for about 15 seconds it is going to lower or reduce a microbial load in a sample but it's not going to get rid of all forms of microbial life the short burst of heat does not disrupt or affect the flavor or the quality of the food product so a lot of times we see pasteurization with things like apple juice and milk we can also ultra pasteurized and that is where we go for an extremely high temperature 134 degrees celsius for an even shorter time so instead of 15 seconds we kick this down to about two to five seconds again pasteurization disinfection boiling water disinfection anything like the autoclave and the tyndalization can be sterilization so moist heat kind of goes either or sterilization or disinfection we also talk about dry heat and i mentioned incineration so this is things like flaming your inoculating loop we use sometimes heating coils or open flames and it's basically to oxidize those microbial cells we can also use the dry ovens which puts out a very dry hot air and again designed to coagulate those proteins disrupt the microbial metabolism this is table 11 4 again comparing some of the forms of heat i'm not going to go through these again but take a look at them looking at the moist heat things like autoclaves and tyndalization followed by our disinfection forms pasteurization boiling water and it talks about some of the medical and commercial uses we also have our dry heats the big one here to remember is the incineration things like your bunton burner flame to flame your inoculating loop causing that oxidation of the cells now we're going to move into the effects of cold refrigeration and desiccation or drying cold is what we call microbiostatic so if you remember earlier i mentioned to you the suffix cyto and i said that if we see that suffix cyto that means to kill anytime you see static static means unchanged so a chemical agent that is static is just slowing or stopping the growth of the micro does not kill them just slows their growth so cold things like refrigeration and freezing do not kill they are not cyto they are static so these are used to preserve food or in our case bacterial cultures and media for longer periods of time desiccation on the other hand is where we actually remove water from the cells and we disrupt the metabolic processes so many cells will still retain the ability to grow when the water's reintroduced so we think about the spores a lot of time when a cell like bacillus or clostridium is dehydrated they're going to form that endospore that tough keratin layer that's going to allow them to survive until the stress is removed now we can also take both of these and put these together so if we expose them to cold and we dry them this is what we call lyophilization or freeze drying the method of preservation all right so we've talked about heat we've talked about cold we've talked about desiccation or drying we're going to now transition into our fourth physical method which is radiation and radiation is one of the parts of the spectrum when we talk about different types of light waves so we have everything from our gamma rays and x-rays all the way out to our radio waves and then right here in the middle is this short little span where we find our visible light our roy g biv the light that we can actually visualize with the human eye we have two types of radiation that are used for microbial control we have the ionizing things like gamma and x-rays and the non-ionizing which is our ultraviolet light so let's start first talking about ionizing radiation ionizing radiation is extremely effective because it has a very deep penetrating power and it's able to get very deep through tissues and cells and that's why when you go to the doctor or the dentist and you have an x-ray done they oftentimes put a lead shield on the surfaces of your body to prevent exposure because the x-rays can penetrate your tissues destroy cells and also break down your dna your nucleic acids so that's why you limit the number of x-rays or cat scans and other things that you have because you don't want a lot of those over a very short period of time the amount of cellular death and damage that can occur can be sufficiently great the non-ionizing radiation on the other hand is uh able to impact your genetic material your nucleic acids uv light forms something known as pyrimidine dimers okay so we have different types of nucleic acid bases we think about our a's t's and our c's and g's our pyrimidines are these a's and t's that you see here and basically what happens is non-ionizing radiation gets in during the replication process and you'll notice here that in a normal segment of dna dna our a's and t's match together and our c's and g's match together however if we expose the segment of dna to ultraviolet radiation it's going to form this thymine dimer so these a's and t's you're going to notice now fuse together we basically bond them together so when we go through the process of dna replication and these strands are separated or unzipped so we would basically unzip these down the middle and we would put a new t here a new g here and so on since these t's are now fused into this dimer or this pair it is now not able to unzip in the regular replication process so it's going to cause things like mutations to form in our genetic material so irradiation control is often used with food products and it's important to note that no one of the regulations is that food that is uh that is applied to this method cannot be sold without the irradiation label uh affixed to the product and this is approved in the us for all sorts of meat products things like pork and beef and what it really does is it extends shelf life promotes an opportunity for food to have a longer shelf life it does not damage or affect the quality or the nutritional safety of the food it is just responsible for destroying the microbial life that leads to spoilage finally we talk about filtration and filtration is really responsible for allowing us to pass a gas or liquid through a filter and oftentimes when we talk about liquids if we have a heat sensitive liquid we can utilize a membrane filter to remove microbes in that liquid material filtration is also used we talked about the hepa filters which are able to filter the air this is really important in places like the air and hospital rooms uh to be able to clean the the microbes out of the air we see a lot of these uh commercial units now sold for personal use people are buying these air filters and air purifiers for their homes to actually use that hepa filter to remove the antimicrobial forms from the air in your home so that wraps up our physical agents and we're going to move into form number two which are our chemical agents of control and this is where we find our disinfectants our antiseptics our germers things like our hand soaps and they have many different benefits to using them they work really well even in a low concentration they're able to be mixed with things like water and alcohol and remain stable they don't break down when they're exposed to these uh these materials they're broad spectrum we can use them on both gram positive and gram negative bacteria they can be used across different forms of microbial life and it's low toxicity to us they're really able to get in and penetrate the microbial cells to impact them they are most times non-corrosive meaning that they're not going to eat away at our skin and they're not going to stain our skin and they're incredibly affordable and readily available so we have basically three levels of chemical decontamination we have our high level germicides and what i really want to know when we talk about high level is that they can kill the spores these are used on devices that are not heat sterilizable and are intended to be used in sterile environments such as body tissues we have the intermediate level uh chemical agents which are able to kill fungal spores uh the tubercle bacteria our mycobacterium tuberculosis and our viruses and then we have the low levels these are only going to eliminate our actively growing vegetative bacterial and fungal cells and some viruses so these are going to clean surfaces that touch the skin but not necessarily come into contact with our mucous membranes really really really important slide here these are several factors that affect germicidal activity the four of them happen to be the nature of the material being treated the degree of contamination again we talked about the amount of microbial cells present the time of exposure obviously the longer we leave a chemical agent on a surface the greater its impact is going to be that's why with all of the covet 19 processes they've said spray the chemical agent on the surface let it sit in contact before you wipe it off and then obviously the concentration 100 is going to work a lot more effective than something that has been diluted down to let's say five or ten percent so we're going to go through and talk about several of these different chemical agents tonight uh chlorines iodines which we'll get into our iodophores our phenols and chlorhexidine which is used a lot in the hospital said setting as a pre-surgical cleanser we also talk about our alcohols hydrogen peroxide so these are many of the ones that we're going to get into so let's start getting into some of these different germicidal categories so the first group we're going to get into are the halogens and the halogens are actually a group on the periodic table and these are things like chlorine and fluorine and bromine all of these chemical agents and specifically the one we're going to talk about is chlorine are also known as the hypochlorites things like chlorine and bleach and the chlor amines they denature proteins and they do this by breaking down a what's called a disulfide bond oftentimes you get two sulfurs that connect together they call it a disulfide bridge or disulfide bond they break apart that disulfide bond causing the protein to lose its shape these are intermediate level disinfectants again can oftentimes be used on if we go back to our previous slide these are going to target things like the fungal spores and the tubercle bacteria and they will utilize to be cleaning devices that will come into contact with our mucous membrane we have iodine which are also known as our iodophores and our iodophores are complexes of iodine and a polymer and a polymer is just a long chain of repeating subunits again these interfere with the disulfide bonds of proteins and these are milder medical and dental degerming agents um oftentimes the when we talk about that complex of the iodine and the polymer that increases the penetration of the iodophores and as we mentioned it's it's less prone to irritating tissues so betadine is an example of an iodophore that uses this iodine so here's an example of cantaloupes being disinfected with chlorine to destroy salmonella that may be carried on their surfaces here's our patient being treated with a povidone iodine solution again those those iodophores um you know things like betadine which are are less prone to irritating or staining tissues we have the phenols the phenols are responsible for either denaturing proteins or destroying the cytoplasmic membranes of cells and these are not only bactericidal um they are fungicidal and virus but they do not destroy spores so things like lysol and uh triclosan and we'll we'll talk about triclosan a little more in a second uh triclosan is an antibacterial additive that's been put into a lot of enzose however there are some significant concerns with triclosan in its use first of all there is no data or limited data at this point to basically suggest the effectiveness of triglyceride it is known to interfere with the populations of the normal flora on your skin we've also seen situations where it causes the growth of resistant bacteria and can even cause some disruption to your hormone levels um on your body so again a lot of the triclosan has started to be removed as the additive to hand soaps so this toxicity of these phenols is starting to make folks question their utes as an antiseptic we have our chlorhexidine and chlorhexidine is an organic base and it contains a chlorine and also a pair of phenol rings and this is used a lot for hand washing it's used as a pre-surgical cleanser and it's even used in wound degerming treating and preventing infections at incision sites or wound sites chlorhexidine is often known as hibiclens and we've already mentioned many of the different types of applications again the pre-operative scrubs the wound cleaning we have the alcohols alcohols are great d germers 50 or higher concentrations can actually dissolve lipids in a membrane and you can use them by disinfecting objects in a soaking nature very high concentrations when we're talking getting up to about 90 95 percent alcohol concentration can actually denature proteins alcohols are not effective against things like non-enveloped viruses and even endospores there's a difficulty of destroying them with alcohols we have hydrogen peroxide hydrogen peroxide is a very highly reactive hydroxyl free radical and its job is to basically um it will eventually decompose to oxygen gas it is incredibly toxic microbes that are anaerobic that cannot survive in the presence of oxygen so many uh microbial cells actually have an enzyme known as catalase and catalase is responsible for breaking down hydrogen peroxide into oxygen gas which is less toxic so these highly reactive hydroxy radicals things like superoxide and hydrogen peroxide can be damaging to microbial cells stronger solutions can actually damage spores as well the effectiveness of hydrogen peroxide actually increases greatly when it's used in combination with things like per acetic acid the aldehydes and the one that we're really going to focus on is this first one here this glutaraldehyde again targets the proteins and the nucleic acids the dna these are intermediate to high level um in chemical agents and glutaraldehyde is actually used as a steroid for heat sensitive equipment so again very high level steroid um used to treat materials that are are heat sensitive formaldehyde on the other hand again can be used as a preservation pool it's toxicity uh toxicity excuse me limits its use again it's extremely toxic to the human body and then we look at things like our gases one of the big gases that we talk about a lot is ethylene oxide or eto and ethylene oxide is often used as a sterilizing gas in a chamber and it is so uh highly sterile in that it actually is sporocytal it's able to destroy spores this is an extremely high level um chemical agent and it is used to sterilize and disinfect plastics and even pre-packaged foods we also have our detergent and soaps detergents are for the most part very ineffective against things like mycobacterium tuberculosis um polar these these molecules are polar and they act as surfactants meaning that they can actually remove the lipids from a cell membrane we talk about um the detergents things like these coronary ammonia compounds the uh coronary ammonia compounds are cationic or positively charged detergents that are often used to wash surfaces and they change that membrane permeability again as surfactants they remove those lipids soaps are alkaline compounds very basic ph higher than 8 all the way up to 14 and they are designed for this mechanical removal of soils and grease containing microbes we also have the heavy metals and the heavy metals are usually things of solutions of silver and mercury are two of the big heavy metals that are able to kill vegetative cells i used to do an experiment um when i was teaching in graduate school with my microbiology students where we would actually uh streak a petri dish with some bacterial cells and then we would put a penny in the center of the plate and let it grow and what you would notice is you would get this zone of clearing the zone of inhibition around the penny because the heavy metals that were emitted from that penny actually had an antimicrobial effect we call this inhibition a lego dynamic action very low level uh chemical agents and a lot of times we're talking about things like martha lates silver nitrate silver nitrate is used as a topical agent oftentimes uh like an eye drop that's put into newborn eyes um and then also silver so again silver mercury merthilate silver nitrate all very effective heavy metals used to inactivate proteins we can also use some different dyes as antimicrobial agents and they are very effective against not only the gram positives but fungi as well the acids and alkalis the you know again ph very low level of activity they prevent spore germination acetic acid can actually inhibit bacterial growth lactic acid is another one that can prevent anaerobic bacterial growth so again table 11 1113 is going to walk you through uh several different uh antimicrobial products that are on the market today what the specific chemical agent is in them and the antimicrobial category i'm not going to ask you this on an exam this is more of an fyi for you so with that being said that's the end of chapter 11. if you have questions feel free as you read as you watch the lecture video bring them to this week's office hours and i'll be more than happy to answer them for you or drop me an email or question and the questions to instructor and i will be more than happy to answer your question or uh elaborate further on any topics have a great week and look forward to seeing you soon