Understanding Microbial Control Techniques ch 13

As we continue in our microbiology course, we're now going to move to chapter 13 and discuss how we can control microbial growth. Now one thing to remember as we go through this chapter is we're not necessarily thinking just about killing the microbes. We're thinking about sometimes how can we control or keep the microbes from growing anymore. Are there times when maybe we need to just stop the growth? Are there times when we do need to kill every microbe? So we just really need to think about that. And when we use the term growth, we're referring to increase in number of microbes. So we aren't talking about the size of the microbe getting any bigger. When we think about controlling microbial growth, there's a few things to consider. What we're trying to do is going to determine which method we choose. So the majority of this chapter, we're going to go through different methods and talk about what different situation is going to help us figure out which method is best. There are going to be some microbes and some parts of microbes, such as endospores, that are much more resistant than others. So that's really going to also... affect which of the choices we are going to go for when we're trying to control this growth. Typically, the majority of these methods of microbial growth are trying to prevent the spread of disease. Believe it or not, the word sterilization is a little bit hard to come by, especially for just a normal consumer in everyday life. Sterilization is difficult. What we are really doing is trying to just get rid of the microbes that are most likely to cause us disease. One thing that's covered in this chapter and nowhere else in the textbook, so I want to make sure we go over, are the different biological safety levels. These are different levels that were established by the Center for Disease Control and the National Institutes of Health to help us determine the level of cleanliness when we're looking at laboratory settings, and things of that nature. So the BSL scale goes from a level one to a level four. Level one is going to be the level where we have our non-pathogenic strains. These are going to be microbes that don't really cause disease under normal conditions. They're of minimal risk. When you move into the BSL or biological safety level two, this is where you get to microbes that can cause disease and sometimes the disease can be severe but these are going to be diseases that you have to be in a certain environment for them to to be of harm to you so we're increasing the danger level of the microbes some and we're just really at this point have to be aware of what we're working with When we move into level three and four, that's when we get to diseases that are much more severe, much more likely to cause disease, and these can be lethal or fatal diseases. One of the main differences between level three and level four is level four a lot of times has your aerosol transmitted infections. So these are diseases that really don't have cures and They can be spread simply by breathing. When you get to the safety level four, HEPA filters, which we'll talk about in this chapter, are required to even filter the air in those levels. So within this chapter we need to understand terminology. So I've already used the term sterilization a little bit as I've gone through these notes. Sterilization is the complete removal or killing of all life. This includes living vegetative microbial cells, endospores, viruses, everything. We really only see sterilization in laboratories and medical facilities. We don't have the ability to sterilize in our homes. So for example, if I wanted to clean something in my house or I wanted to I have a wound that I'm cleaning or something like that. I can't sterilize that. That is not something that can be accomplished. Most of the methods of sterilization are going to be physical methods that we'll go through. There are a few chemicals called sterilants that can sterilize, but those are much harder to come by. The things that we as normal consumers do on an everyday basis are not sterilization. They fit more into the following categories on this slide. A lot of the things that we do in our household is considered disinfection. So disinfection is going to inactivate your microbes that are typically found on the surfaces of fomites using some sort of chemical or heat. Now, this might be the first time we've used the term fomite in this particular class. A fomite is any non-living object, things like doorknobs, toys, that might harbor a pathogen. So what would be some examples of disinfection? If you've used bleach or bathroom cleaner to clean your house, you've disinfected that house. If you've sprayed Lysol on something, you've disinfected. There are still microbes that are living, but hopefully you got all the dangerous ones. Antiseptics are antimicrobial agents that can disinfect, but they disinfect on living skin. Antisepsis will be things like alcohol, hydrogen peroxide. So if you put alcohol on the skin before an injection occurs, that would be an antisepsis. Degerming involves physically scrubbing to remove microbes. Even if you use soap, it's the physical rubbing together of the hands that remove microbes. And so talking about that injection, if you didn't just put alcohol on the surface but you actually took a cotton swab and rubbed an area after you swabbed with alcohol, then you've not only used an antisepsis technique, you've degermed the area as well. Sanitation is a term that's used to describe cleaning of fomites that's removing just enough of the microbes that you're now at a level that we would consider safe for public health. That's going to be things like commercial dishwashers, looking at surfaces in hospitals. Those are all going to be sanitized. This table comes from your book and I think it's just a really good way for you to study and make sure you can recognize some different situations and put them into the correct category of disinfection, sanitation, sterilization, antisepsis, and de-germing. So I highly recommend that you read through this table. So a little bit more terminology. A lot of times you'll see words that end with the suffix side and static. If you see the term side, that means you're killing your target microbe. So a bacteriocide is going to be something that can kill bacteria. Viricide can kill a virus. Fungicide kills a fungus, so kills a mold, something like that. The suffix static tells us we're not necessarily going to kill what microbe we're after, but we may stop its growth. So something may be bacteriostatic. Why would we want something that's only static? Why not just kill it all? Sometimes we don't want to kill all the microbes, but also a lot of your materials that can kill microbes are pretty toxic to humans and animals. So we just have to be really careful when we're using those. So let's go through the different methods. Physical methods of control will be first, and first we're going to look at heat. heat, we can look at what temperature can allow us to kill the correct amount of microbes, or we can also look at how long does it take us to kill microbes if we have a certain temperature. It may surprise you that one of the most common methods we use in everyday life that we think is controlling microbes, microbial growth, boiling, is really not that useful of a technique. Boiling can only kill living bacterial cells and some viruses. But no matter how long you boil, you cannot kill endospores. You can't kill all viruses. It can really trick you into thinking you've accomplished something. So, boiling baby bottles and things like that, a lot of parents like to think that they're sterilizing those baby bottles when in fact they're not sterilizing. They're just... Killing a few things. There are some methods of heat that we can use to sterilize and there's two ways we can do that. So both things listed on this slide are sterilization. We can incinerate. Incinerate simply means putting something directly into the flames. We can also use a machine called an autoclave. An autoclave combines high temperature and high pressure. For a specific amount of time, autoclaves can actually even kill endospores. The way the autoclave works, if you look at this picture here, it's got a chamber with a nice door that seals shut. So you put your specimen you want to sterilize into the autoclave right here in the center and then it's going to increase in pressure in this area while steam is pumped in. So we can get the temperature of 121 degrees Celsius, that's 21 degrees Celsius above boiling temperature, plus 15 pounds per square inch pressure, and it has to stay at that temperature and that pressure for 15 minutes. Then it's considered sterilized. This is an important number series for you to remember. The method of heat that does not sterilize is pasteurization. Pasteurization just kills pathogens to try to keep things that you pasteurize to last longer. There's different types of pasteurization. You know, you may have noticed you can buy milk in a jug in the refrigerator and it's going to last for a couple weeks. But you can also buy milk in these containers. It doesn't even have to go in the refrigerator and it can last for months. and that's just in the different way that it's pasteurized. But no matter how it's pasteurized, it is never sterile. All right, so other than heat, what are some methods we can use to control? Well, what does cold do for us? If you put something in the refrigerator, does that sterilize it? Well, of course not. It's not going to sterilize it just by putting it in the refrigerator, but it can slow down the growth of microbes to make your food last longer. Pressure is sometimes used. It can kill some microbes, make things last a little longer on grocery store shelves. We do that. Sometimes we'll dry out foods, things like raisins that dries out a grape, pulls the water out, preserves your food, beef jerky. Things like that can make your food last longer. Osmotic pressure is the fancy way of saying if we add enough sugar or salt, we can increase shelf life. And if any of you have ever made jelly or you've eaten jellies, you know they're very sweet. All that sugar is put in there, not really for taste, we like the way it tastes, but it's put in there to keep microbes from growing. All right, what about radiation? There's two different types of radiation. One type of radiation that does sterilize is this one, ionizing radiation. Ionizing radiation is strong enough to pass through a cell and damage the components, allowing it to sterilize. Ionizing radiation is going to be something like x-ray, gamma radiation. We use this to sterilize a lot of medical equipment that's packaged into plastic and things like that. Non-ionizing radiation will be things like ultraviolet light. It really doesn't sterilize that great. It can't penetrate through anything. A lot of times we will use non-ionizing radiation in water filtration systems kind of as a backup to our filter. And also in some of your hospital settings, certain hoods and different equipment will hit with ultraviolet light to kill some of those microbes that could cause damage. Filtration is a method of physically removing microbes, not killing them. We have HEPA filters, high efficiency particulate air filters. A HEPA filter cleans the air. And then we have membrane filters, which filter liquids. So why would we want to use a filter? Well, for the air, it's one of the best methods that we have. For a liquid, filtration may be needed if we have a liquid that can't be heated. That liquid can be heated and we want to sterilize, we're going to put that liquid in the autoclave. but if we can't heat it something like antibiotics sometimes our only option is to filter so the last thing i wanted to spend a little time talking to you about are what are some of the chemical methods we can use to control microbial growth well joseph lister was the first one to discover that you could use chemicals to disinfect he used a chemical called phenol to treat surgical wounds and his patients started living a lot longer than anybody else's Well, it turns out phenol burns the skin. It's pretty rough. So we don't use phenols anymore. Now we use chemicals called phenolics. Things like thymol and eucalyptol, they come from plants. Creosote, you may have heard your grandma talk about that one. Lysol, Physio-X, which is a surgical scrub. Triclosan, that's found in antibacterial hand soaps like Dial Soap. Those are all phenolics and they do kill some microbes. Sometimes we incorporate heavy metals like mercury, silver, copper, or zinc into things because the metals will interfere with the normal growth of microbes and slow them down a little bit. We use halogens. Halogens are going to be iodine and chlorine. We've all used bleach before. Some of you may have had that grandmother that used iodine. If you fell and scraped your knee, they'd rub the brown stuff on you that burned so bad. That was iodine. Alcohol serves as a chemical that can control growth of microbes. It turns out though that alcohol is most efficient at 70% not 100%. Alcohol has been overused quite a bit recently with the popularity of alcohol hand sanitizers. Those should really only be used if proper hand washing can't be completed. And then the bispoquinides are very commonly used in surgical scrubs. So you may see those if you end up working in a hospital setting. And then the last one are alkylating agents. The one I want to talk to you about is ethylene oxide. It is considered to be the only chemical gas sterilant. So that is a chemical that if used properly can sterilize and we do use that in the hospital setting. So the types of questions you need to be prepared to answer will be which of the methods are able to sterilize. which methods can't and then I'm going to ask you questions and see if you can think about what would be the best technique used in different situations. So really try to think about this a little and good luck studying.

So we just really need to think about that. And when we use the term growth, we're referring to increase in number of microbes. So we aren't talking about the size of the microbe getting any bigger. When we think about controlling microbial growth, there's a few things to consider. What we're trying to do is going to determine which method we choose.

So the majority of this chapter, we're going to go through different methods and talk about what different situation is going to help us figure out which method is best. There are going to be some microbes and some parts of microbes, such as endospores, that are much more resistant than others. So that's really going to also...

affect which of the choices we are going to go for when we're trying to control this growth. Typically, the majority of these methods of microbial growth are trying to prevent the spread of disease. Believe it or not, the word sterilization is a little bit hard to come by, especially for just a normal consumer in everyday life. Sterilization is difficult. What we are really doing is trying to just get rid of the microbes that are most likely to cause us disease.

One thing that's covered in this chapter and nowhere else in the textbook, so I want to make sure we go over, are the different biological safety levels. These are different levels that were established by the Center for Disease Control and the National Institutes of Health to help us determine the level of cleanliness when we're looking at laboratory settings, and things of that nature. So the BSL scale goes from a level one to a level four.

Level one is going to be the level where we have our non-pathogenic strains. These are going to be microbes that don't really cause disease under normal conditions. They're of minimal risk.

When you move into the BSL or biological safety level two, this is where you get to microbes that can cause disease and sometimes the disease can be severe but these are going to be diseases that you have to be in a certain environment for them to to be of harm to you so we're increasing the danger level of the microbes some and we're just really at this point have to be aware of what we're working with When we move into level three and four, that's when we get to diseases that are much more severe, much more likely to cause disease, and these can be lethal or fatal diseases. One of the main differences between level three and level four is level four a lot of times has your aerosol transmitted infections. So these are diseases that really don't have cures and They can be spread simply by breathing. When you get to the safety level four, HEPA filters, which we'll talk about in this chapter, are required to even filter the air in those levels. So within this chapter we need to understand terminology.

So I've already used the term sterilization a little bit as I've gone through these notes. Sterilization is the complete removal or killing of all life. This includes living vegetative microbial cells, endospores, viruses, everything.

We really only see sterilization in laboratories and medical facilities. We don't have the ability to sterilize in our homes. So for example, if I wanted to clean something in my house or I wanted to I have a wound that I'm cleaning or something like that. I can't sterilize that.

That is not something that can be accomplished. Most of the methods of sterilization are going to be physical methods that we'll go through. There are a few chemicals called sterilants that can sterilize, but those are much harder to come by. The things that we as normal consumers do on an everyday basis are not sterilization. They fit more into the following categories on this slide.

A lot of the things that we do in our household is considered disinfection. So disinfection is going to inactivate your microbes that are typically found on the surfaces of fomites using some sort of chemical or heat. Now, this might be the first time we've used the term fomite in this particular class. A fomite is any non-living object, things like doorknobs, toys, that might harbor a pathogen.

So what would be some examples of disinfection? If you've used bleach or bathroom cleaner to clean your house, you've disinfected that house. If you've sprayed Lysol on something, you've disinfected.

There are still microbes that are living, but hopefully you got all the dangerous ones. Antiseptics are antimicrobial agents that can disinfect, but they disinfect on living skin. Antisepsis will be things like alcohol, hydrogen peroxide. So if you put alcohol on the skin before an injection occurs, that would be an antisepsis.

Degerming involves physically scrubbing to remove microbes. Even if you use soap, it's the physical rubbing together of the hands that remove microbes. And so talking about that injection, if you didn't just put alcohol on the surface but you actually took a cotton swab and rubbed an area after you swabbed with alcohol, then you've not only used an antisepsis technique, you've degermed the area as well. Sanitation is a term that's used to describe cleaning of fomites that's removing just enough of the microbes that you're now at a level that we would consider safe for public health. That's going to be things like commercial dishwashers, looking at surfaces in hospitals.

Those are all going to be sanitized. This table comes from your book and I think it's just a really good way for you to study and make sure you can recognize some different situations and put them into the correct category of disinfection, sanitation, sterilization, antisepsis, and de-germing. So I highly recommend that you read through this table. So a little bit more terminology.

A lot of times you'll see words that end with the suffix side and static. If you see the term side, that means you're killing your target microbe. So a bacteriocide is going to be something that can kill bacteria. Viricide can kill a virus.

Fungicide kills a fungus, so kills a mold, something like that. The suffix static tells us we're not necessarily going to kill what microbe we're after, but we may stop its growth. So something may be bacteriostatic. Why would we want something that's only static? Why not just kill it all?

Sometimes we don't want to kill all the microbes, but also a lot of your materials that can kill microbes are pretty toxic to humans and animals. So we just have to be really careful when we're using those. So let's go through the different methods. Physical methods of control will be first, and first we're going to look at heat.

heat, we can look at what temperature can allow us to kill the correct amount of microbes, or we can also look at how long does it take us to kill microbes if we have a certain temperature. It may surprise you that one of the most common methods we use in everyday life that we think is controlling microbes, microbial growth, boiling, is really not that useful of a technique. Boiling can only kill living bacterial cells and some viruses.

But no matter how long you boil, you cannot kill endospores. You can't kill all viruses. It can really trick you into thinking you've accomplished something.

So, boiling baby bottles and things like that, a lot of parents like to think that they're sterilizing those baby bottles when in fact they're not sterilizing. They're just... Killing a few things.

There are some methods of heat that we can use to sterilize and there's two ways we can do that. So both things listed on this slide are sterilization. We can incinerate.

Incinerate simply means putting something directly into the flames. We can also use a machine called an autoclave. An autoclave combines high temperature and high pressure.

For a specific amount of time, autoclaves can actually even kill endospores. The way the autoclave works, if you look at this picture here, it's got a chamber with a nice door that seals shut. So you put your specimen you want to sterilize into the autoclave right here in the center and then it's going to increase in pressure in this area while steam is pumped in. So we can get the temperature of 121 degrees Celsius, that's 21 degrees Celsius above boiling temperature, plus 15 pounds per square inch pressure, and it has to stay at that temperature and that pressure for 15 minutes. Then it's considered sterilized.

This is an important number series for you to remember. The method of heat that does not sterilize is pasteurization. Pasteurization just kills pathogens to try to keep things that you pasteurize to last longer. There's different types of pasteurization. You know, you may have noticed you can buy milk in a jug in the refrigerator and it's going to last for a couple weeks.

But you can also buy milk in these containers. It doesn't even have to go in the refrigerator and it can last for months. and that's just in the different way that it's pasteurized.

But no matter how it's pasteurized, it is never sterile. All right, so other than heat, what are some methods we can use to control? Well, what does cold do for us?

If you put something in the refrigerator, does that sterilize it? Well, of course not. It's not going to sterilize it just by putting it in the refrigerator, but it can slow down the growth of microbes to make your food last longer. Pressure is sometimes used.

It can kill some microbes, make things last a little longer on grocery store shelves. We do that. Sometimes we'll dry out foods, things like raisins that dries out a grape, pulls the water out, preserves your food, beef jerky.

Things like that can make your food last longer. Osmotic pressure is the fancy way of saying if we add enough sugar or salt, we can increase shelf life. And if any of you have ever made jelly or you've eaten jellies, you know they're very sweet. All that sugar is put in there, not really for taste, we like the way it tastes, but it's put in there to keep microbes from growing.

All right, what about radiation? There's two different types of radiation. One type of radiation that does sterilize is this one, ionizing radiation.

Ionizing radiation is strong enough to pass through a cell and damage the components, allowing it to sterilize. Ionizing radiation is going to be something like x-ray, gamma radiation. We use this to sterilize a lot of medical equipment that's packaged into plastic and things like that. Non-ionizing radiation will be things like ultraviolet light. It really doesn't sterilize that great.

It can't penetrate through anything. A lot of times we will use non-ionizing radiation in water filtration systems kind of as a backup to our filter. And also in some of your hospital settings, certain hoods and different equipment will hit with ultraviolet light to kill some of those microbes that could cause damage. Filtration is a method of physically removing microbes, not killing them. We have HEPA filters, high efficiency particulate air filters.

A HEPA filter cleans the air. And then we have membrane filters, which filter liquids. So why would we want to use a filter? Well, for the air, it's one of the best methods that we have. For a liquid, filtration may be needed if we have a liquid that can't be heated.

That liquid can be heated and we want to sterilize, we're going to put that liquid in the autoclave. but if we can't heat it something like antibiotics sometimes our only option is to filter so the last thing i wanted to spend a little time talking to you about are what are some of the chemical methods we can use to control microbial growth well joseph lister was the first one to discover that you could use chemicals to disinfect he used a chemical called phenol to treat surgical wounds and his patients started living a lot longer than anybody else's Well, it turns out phenol burns the skin. It's pretty rough. So we don't use phenols anymore.

Now we use chemicals called phenolics. Things like thymol and eucalyptol, they come from plants. Creosote, you may have heard your grandma talk about that one.

Lysol, Physio-X, which is a surgical scrub. Triclosan, that's found in antibacterial hand soaps like Dial Soap. Those are all phenolics and they do kill some microbes.

Sometimes we incorporate heavy metals like mercury, silver, copper, or zinc into things because the metals will interfere with the normal growth of microbes and slow them down a little bit. We use halogens. Halogens are going to be iodine and chlorine. We've all used bleach before.

Some of you may have had that grandmother that used iodine. If you fell and scraped your knee, they'd rub the brown stuff on you that burned so bad. That was iodine.

Alcohol serves as a chemical that can control growth of microbes. It turns out though that alcohol is most efficient at 70% not 100%. Alcohol has been overused quite a bit recently with the popularity of alcohol hand sanitizers. Those should really only be used if proper hand washing can't be completed. And then the bispoquinides are very commonly used in surgical scrubs.

So you may see those if you end up working in a hospital setting. And then the last one are alkylating agents. The one I want to talk to you about is ethylene oxide.

It is considered to be the only chemical gas sterilant. So that is a chemical that if used properly can sterilize and we do use that in the hospital setting. So the types of questions you need to be prepared to answer will be which of the methods are able to sterilize.

which methods can't and then I'm going to ask you questions and see if you can think about what would be the best technique used in different situations. So really try to think about this a little and good luck studying.

Transcript for:Understanding Microbial Control Techniques ch 13

Transcript for:
Understanding Microbial Control Techniques ch 13