Physical Methods to Control Microbial Growth - Video Tutorials & Practice Problems

Physical Methods to Control Microbial Growth

in this video we're going to begin our lesson on the physical methods to control microbial growth. And so it turns out that there are actually many different types of physical methods to control microbial growth. And down below we have an image that represents our map of the lesson or our outline of the lesson. Moving forward in our course on the physical methods to control microbial growth. And so moving forward in our course, we're going to be following this map or this outline by following the left most branches first. And so we'll talk about temperature as a physical method. Talking about dry heat, incineration and hot air ovens and also moist heat such as boiling pasteurization and autoclaves. And then we'll also talk about using temperature but using low temperatures such as refrigeration and freezing. And then after we cover the temperature. Then we'll move on to the next type of physical method which is drying and that includes techniques such as desiccation and liable ization. Then we'll move on to filtration such as liquid filters and air filters. And we'll also talk about high pressure processing H. P. P. And last but not least, we'll talk about irradiation and the two main types which are ionizing radiation and non ionizing radiation. And so we'll move forward in our lesson covering these topics in this particular order. And we'll get to learn a lot more about each of these physical methods as we move forward in our chorus. But for now this year concludes our brief introduction to some of the physical methods to control microbial growth. And I'll see you all in our next video to talk more about temperature, physical control, specifically dry heat. See you all there.

Dry Heat

in this video, we're going to begin our lesson on dry heat as a physical method to controlling microbial growth. And so dry heat is simply heat that has no moisture or no liquid content. Thus that's why it's called dry heat. Now, incineration is a type of dry heat, which is referring to the destruction by burning with a direct flame. And that is of course going to turn the cell components into ashes. Now, hot air ovens is another way to deliver dry heat. And as their name implies, these are going to be ovens that kill microbes with dry heat by destroying cell components and denature ring proteins or inactivating proteins. Now, dry heat in general typically requires higher temperature and more time to kill microbes than moist heat does. And we'll get to talk more about moist heat in our next lesson video. But really what we're trying to say here is that moist heat can kill microbes faster and with lower temperatures than dry heat does. However, an advantage of using dry heat over moist heat is that dry heat can actually be used on some moisture sensitive items that don't work well with moisture, such as for example, powder and oils will not be able to be used with moist heat because it can change their composition and also just uh they're not compatible. However, dry heat can be used on them. And so if we take a look at our image down below notice on the left hand side, we're showing you a laboratory tool right here being burnt with a direct flame. And so this is a form of incineration of a laboratory tool to help control the microbial growth on this laboratory tool. Over here on the right, what we're showing you is a hot air oven and the hot air oven is going to be killing microbes on laboratory instruments. And so laboratory instruments that are not sensitive to heat can be placed inside of this hot air oven and they can be um the microbial growth can be controlled with this hot air ovens. And so this is once again a form of dry. These are forms of dry heat, which is heat that has no moisture or no liquid content. And so this year concludes our brief lesson on dry heat as a physical method to controlling microbial growth. And we'll be able to get some practice and learn more about other physical methods of controlling microbial growth as we move forward in our course. So I'll see you all in our next video.

Moist Heat

in this video, we're going to begin our lesson on moist heat as a physical method to controlling microbial growth. And so most microbes require really specific temperatures in order for normal growth and reproduction to occur and exceeding those temperatures by applying heat. Either dry heat or moist heat can destroy microbes. Now, moist heat is specifically a form of heat that is going to have moisture as its name implies, or you can define it also as a heat that has liquid content in it. Now moist. He is capable of killing microorganisms by irreversibly de nature during their enzymes and proteins now moist. He is also typically going to be more effective than dry heat and that is because moist heat generally requires lower temperatures and less time to kill microbes than dry heat. Dry heat usually takes longer to kill microbes and it requires higher temperatures generally. Now, examples of moist heat include boiling uh pasteurization, which is really just brief heat treatment, and it also includes pressurized steam. Now, later in our course, we're going to talk a little bit more about pasteurization, this brief heat treatment. But what you should know about pressurized steam is that an instrument or device known as an auto clave is a device that somewhat resembles a pressure cooker and it's going to be using high temperatures and pressurized steam in order to sterilize heat and moisture, moisture tolerant items. And so if we take a look at our image down below, we can get a better understanding of moist heat. And so an example of moist heat or uh examples include boiling by simply just having liquid heated to a high temperature and boiling. It also pasteurization, which is a brief heat treatment. And here we're showing you an image of milk being pasteurized. And once again we'll get to talk more about pasteurization in our next lesson video and then also using pressurized steam by using a device known as an auto clave. And so here is a diagram of what an autoclave can look like. It's going to have the ability to bring in heat and steam. And the steam is going to create lots of high pressures and heat moist heat in order to sterilize uh items that are heat and moisture tolerant. And the waste errands theme is able to come out the back end over here. Now, over here on the right, what we're showing you as a table that shows you that dry heat typically requires a lot more time to sterilize in comparison to moist heat. And so if you're using the same temperature of 121°C noticed that moist, he is able to kill more effectively. It takes a lot less time, only 15 minutes here to kill or to sterilize the item. In comparison to the 600 minutes or 10 hours when using dry heat. And so once again, this just shows that moist he is more effective uh than dry heat. However, once again, there are advantages and disadvantages to each of these methods. And even though moist, he can be more effective, moisture is not always going to be compatible with the item to be treated. And so sometimes dry. He is a better method simply because of the compatibility of the items. Uh And so this year concludes our brief lesson on moist heat and once again, we'll be able to apply these concepts and learn more about pasteurization and other physical methods to control microbial growth as we move forward in our course. So I'll see you all in our next video.

Moist Heat:Pasteurization

In this video, we're going to continue to talk about moist heat as we talk more about pasteurization. And so pasteurization is a process that was first discovered by Louis Pastor and it was also named after louis Pasteur as well as you can see uh in the naming. And so pasteurization refers to the brief boiling of a specific product, such as for example, milk or wine in order to disinfect it and make it safe for consumption without significantly changing its properties such as its taste or its flavor. Now, most pasteurization is completed by the method known as high temperature short time method, or H. T. S. T. Method for short, Which is going to expose the product to temperatures of about 165°C for only about 15 seconds. Now, the temperature used in high temperature short time or H. T. S. T. Is not typically high enough to sterilize the product and so some microbes are typically going to remain even after the HD SDI pasteurization method is implemented. However, another method implements even higher temperatures and even shorter times than the HD SDI method. And this is the ultra high temperature or uht pasteurization method which uses such high temperatures that it's capable of actually sterilizing the product and killing all of the microbes. And so for example, the uht method would use temperatures that are up to degrees Celsius for just three seconds. And so if we take a look at our image down below, we can get a better understanding of the H. D. S. T. And the uht pasteurization methods which once again were first discovered by louis Pasteur. And so notice here that we have some milk here that is being extracted from this cow. Uh Here's the milk being extracted from the cow and the milk originally when it's extracted from the cow is going to have many different types of microorganisms in it and it may be unsafe to drink directly. And so pasteurization is a process that helps control the microbial growth in the milk. And so there are two methods of pasteurization. Once again, there's the high temperature short time method or the H. T. S. T. Method, which is being implemented towards the top here and that's going to be using temperatures of around 165 degrees Celsius for somewhere between 10 to 20 seconds. And so this allows us to get milk that is safe to consume without significantly changing the flavor and the taste of the milk. However, because the H. T. S. T. Method does not use temperatures high enough for sterilization, it is still important that we need to implement preservation techniques such as refrigeration in order to help delay the growth of the microbes. And so lots of milk that is refrigerated is going to have gone through the HTS T pasteurization method. Now down below on the bottom half of the image. What we're showing you is the ultra high temperature pasteurization method or the U. H. T. Method and notice that this method is going to use much higher temperatures around 280 degrees Celsius for a shorter times just three seconds. But the high temperatures are high enough to create a to sterilize to kill all of the microbes. And therefore this milk is actually capable of being shelf safe milk being stored on a shelf and it does not need to be refrigerated. And so sometimes you can go into the grocery store and find some milk that is just stored on a shelf and so it can be stored at room temperature because the milk has undergone uh this U. H. T. Uh method of pasteurization. And so this year concludes our brief lesson on pasteurization and we'll be able to get some practice applying these concepts and learn more about other physical methods of controlling microbial growth as we move forward in our course. So I'll see you all in our next video.

Pasteurization is what type of microbial control method?

• A. A physical, dry heat control method.
• B. A chemical, heat control method.
• C. A physical, moist heat control method.

Low Temperatures

So now that we've talked about both dry heat and moist heat as a means of controlling microbial growth. In this video, we're going to talk about using low temperatures as a physical method to controlling microbial growth. And so depending on the type of microbe, low temperatures can have varying effects because recall that some microbes are capable of growing really well at low temperatures. However, generally low temperatures are going too slow the growth of microorganisms. And so recall from our previous lesson videos that psych profiles and psy crow troughs are groups of microbes that are exceptions because They are actually capable of growing pretty well at freezing temperatures below 0°C. Now, other than these exceptions, most other organisms are going to generally grow slower with lower temperatures. And so low temperatures can be in many cases uh sufficient means of controlling microbial growth. Now refrigeration generally is going to delay or once again slow the growth of many pathogens and spoilage microbes, which is why a lot of times we refrigerate many of our foods in order to help delay the growth and slow the growth until we're able to eat those items. And we can store those items in a refrigerator for longer periods of time by keeping them at these low temperatures. Now freezing usually is going to preserve foods and other products by inhibiting the microbial growth, but freezing does not always kill the microorganisms. And so sometimes you're able to freeze foods and other products and it can really extend the life of those items by a lot. But once you thaw those items because the microbial growth is only being inhibited by the cold temperatures, um sometimes thawing them will allow those microbes to continue to grow um after those items have been thought. And so recall from our previous lesson videos that the term preservation is referring to the process of delaying the spoilage of perishable products and perishable products once again are items that are likely to go bad quickly, such as specific types of vegetables and fruits and things like that. And so if we take a look at our image down below, we can get a better understanding of how low temperatures can be used as a physical method to controlling microbial growth, specifically refrigeration and freezing. And so on the left hand side over here, what we're showing you is refrigeration and uh refrigeration can be used to store many of our foods that we eat on a daily basis, but also for refrigeration can also be used in a laboratory setting here. This is showing you an image of a cold lab that Um is going to be maintained right around 2°C And experiments are going to be performed at 2°C inside of this cold room uh in this lab Now over here on the right, what we're showing you are images of freezing. And of course freezing is going to imply uh using temperatures below 0°C. And uh lab specimens can be stored in a freezer for really long periods of time because it inhibits the microbial growth completely. In many cases again, except for the exceptions of the psych profiles and psycho troughs. And so generally low temperatures such as refrigeration and freezing is going to help slow the growth of microorganisms. And so it is a means of controlling microbial growth. And so this year concludes our lesson on low temperatures and we'll be able to get some practice applying these concepts and learn more about other physical methods of controlling microbial growth as we move forward in our course. So, I'll see you all in our next video

Desiccation

in this video, we're going to begin our lesson on the process of desiccation and how it is used as a physical method to control microbial growth. And so although some microbes can survive for years without water, most microbes require water at a pretty constant rate in order to grow effectively. And so the process of desiccation is the process of drying out or removing moisture or water from something in order to prevent it from growing effectively. And so generally the process of desiccation results in the inhibition of microbial growth. Now recall from our previous lesson videos when we talked about osmosis and tennis City that the addition of salute such as salt, for example, can create what's known as a hyper tonic environment. And hyper tonic environments are capable of drawing out water from cells via osmosis in order to dehydrate those cells and the dehydration of those cells is generally going to result in the inhibition of the growth. And so if we take a look at our image down below, we can get a better understanding of this process of desiccation, which again is like drying out. And so we have these images of the cactus and the sun to remind you of dried out areas. And so notice over here on the left, we're just showing you an image of desiccated soil again, to help you associate desiccation with drying out over here. What we're showing you is some meat that's actually being salted in order to create a hyper tonic environment on the outside of the meat. And so notice all of the salt that's on the outside of the meat. And this is called salt caring it can help to preserve the meat uh in order to delay microbial growth and inhibit microbial growth. And so essentially what's happening by adding the salt is it creates what's known as a hyper tonic environment which recall from our previous lesson videos as an environment that has more salutes on the outside of the cells. And so water in terms of osmosis always flows from hype a tonic solutions towards hyper tonic solutions. And so if the outside is hyper tonic, water flows towards the outside of the cell via osmosis. And so when water leaves these cells, this dedicates or dries out the cells and basically what we get is what's called a dried out or a cremated red blood cell here. And so ultimately this is going to also happen with microbes as well and that will dry out and dehydrate those microbes and inhibit their growth. And really that's the main idea behind the salting out here is that it helps to inhibit and prevent microbial growth to preserve the meat. And so this year concludes our brief introduction to desiccation as a physical means of controlling microbial growth. And we'll be able to get some practice applying these concepts and learn more about other physical methods of controlling microbial growth as we move forward in our course. So I'll see you all in our next video.

How does desiccation control microbial growth?

• A. Desiccation removes all moisture from living cells, inhibiting or killing microbes.
• B. Desiccation drops the temperature so low, that only psychrophiles can survive.
• C. Desiccation utilizes ultra-heated steam to kill pathogenic microbes.
• D. Desiccation incinerates all living cells, killing all microbes.

Lyophilization

in this video, we're going to introduce liable Ization as a physical method of controlling microbial growth and so liable. Ization is really just the process of freeze drying and so really liable. Ization is freeze drying basically the process of freezing the product and then drying out the product in a vacuum. Now, through the process of liberalization, it is going to remove water from the product via sublimation. And sublimation is referring to the transition of water directly from a solid state to a gas state without actually becoming a liquid. Now lie. A civilization is widely used for preserving foods such as for example, coffee, milk, meats, vegetables, and a lot of other foods as well, without the need for refrigeration. Now, overall, through the process of liberalization, the quality of the product is going to end up being a lot better than usual. Typical drying methods. And so if we take a look at our image down below, at Lyon Equalization notice on the left hand side over here, we're showing you a fancy piece of equipment that is a lab freeze dryer. And here we're showing you some scientists that are using a lab freeze dryer to preserve artifacts with freeze drying or like capitalization. And over here on the right, we're showing you some freeze dried strawberries and some freeze dried ice cream as well. Over here, this is the ice cream and this is the strawberries and so basically liable. Ization is a common means of preserving many different types of foods. And so it is a means of controlling microbial growth through freezing and drying almost a combination of using low temperatures and desiccation. And so this year concludes our brief lesson only awful Ization freeze drying. And we'll be able to get some practice applying these concepts and learn more about other physical methods of controlling microbial growth as we move forward. So I'll see you all in our next video

Filtration

In this video, we're going to talk about filtration as a physical method to controlling microbial growth. And so filtration is the process of using filters with pores that are incredibly small, small enough to actually physically remove microbes from either liquid or air. Now, once again, the pores that are in the filter are incredibly small and their way smaller than the microbes themselves. And so the microbes in relation to the pores are way too large to pass through those pores of the filter. And therefore the microbes are going to get trapped in the filter and that is what separates the microbes from the liquid and air that they are in because the liquid and air can pass through the filter very easily, but the microbes are too large and cannot pass they get trapped. And so filtration can be used to remove microbes from heat sensitive liquids when he is not an option. Now, a very specific type of filter, known as a high efficiency particulate air filter or a HEPA filter, for sure, is a specific type of filter that will remove airborne particles and microbes from the air. And so if we take a look at our image down below, notice that the left hand side over here is focused on liquid filtration, and the right hand side over here is focused on air filtration and so focusing in on the left side. First noticed that we have this apparatus right here and there is a vacuum pump with a flask here and then there's this container at the top and noticed that the container at the top contains the contaminated liquid, but it also contains the filter itself, which is horizontally here in orange color. And so the contaminated liquid is going to have microbes in it along with the liquid. And so zooming into this region. You can see this over here, notice that the microbes are in green. So we can label these as the microbes and the microbes are simply too large to pass through the pores of the filter. And so you can see the microbe filter again is here in orange. And there are some pours in it. But the microbes are too large to get through. However the liquid itself is capable of getting through. And so the liquid is going to pass through this filter. Uh but the microbes are going to get trapped in the filter itself. And so this separates the microbes from the liquid and the liquid that gets through is going to be sterile liquid. And so over here, what we're showing you are some images of um some cells that are being trapped in a filter. And so here at the top we're showing you micro caucus lutece bacteria on a polycarbonate filter. And so notice that these bacterial cells that you see right here are simply too large to pass through these tiny tiny little pores that are neighboring them. And so the microbes get trapped in the filter. But once again the liquid is capable of passing through down below. We're showing you some sperm cells on a polycarbonate filter and again, the sperm cells that you see here are simply too large to pass through these tiny little pores that you see all around them. Now, over here, on the right hand side again, we're showing you air filtration and specifically you want to think about the HEPA filters, the high efficiency particulate air filters. And so HEPA filters are commonly used on airplanes to ensure that the air that you're breathing on airplanes is free of microbes that may be found in the atmosphere. And so here we're showing you the abbreviation for HEPA, uh, is for a high efficiency particulate air filter or a HEPA filter for short. And so this year concludes our brief lesson on filtration as a physical method to control microbial growth by physically removing microbes from liquids or air. And so we'll be able to get some practice applying this concept moving forward and also learn about other physical methods of controlling microbial growth moving forward in our lessons. So I'll see you all in our next video.

High Pressure Processing

In this video, we're going to talk about high pressure processing as a physical method to controlling microbial growth. And so high pressure processing is commonly abbreviated as H. P. P. And high pressure processing or H. P. P. As its name implies is going to be a process that uses really really high pressures somewhere around £120,000 per square inch or P. S. I. Which is a unit of pressure. And it uses these really really high pressures in order to destroy microbes and control microbial growth. And so high pressure processing or H. P. P. Is able to kill microbes by altering the molecular structure of proteins. Now it can also be used to disinfect uh specific products while still preserving features like flavors, colors and nutrient values as well. And so that's a benefit of using H. P. P. Or high pressure processing. Now it is important to also note that some microbes uh specifically endo spores that are capable of tolerating high pressures are going to be able to survive high pressure processing. And so high pressure processing or H. P. P. Does not always kill, it does not always sterilize that particular product. And so if we take a look at our image down below, we can get a better understanding of high pressure processing or H. P. P. And so basically it's going to be a device that is going to create immense amount of pressures and so you can put your item to be treated inside of the instrument and it's going to create extreme amount of pressure. And once again that pressure can ultimately ultra molecular structure of proteins which is going to kill microbes. And so the high pressure is again able to kill uh many microbes but again uh some are able to tolerate high pressures and so it does not always kill all microbes so it's not always going to sterilize. And so this year concludes our brief lesson on high pressure processing as a physical method to controlling microbial growth. And we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Irradiation

in this video, we're going to briefly introduce irradiation as a method of controlling microbial growth. And so irradiation is the process by which an object is exposed to radiation. And so irradiation can be used to destroy microbes and control microbial growth. Now, radiation is defined as the emission or transmission of energy as either electromagnetic waves or as moving subatomic particles. Now in this video, we're going to briefly introduce two types of radiation. The first is ionizing radiation, which is going to be radiation that has penetrative power. It's capable of penetrating deeper into objects. And so this penetrative radiation also has sufficient amounts of energy to remove electrons and therefore as its name implies, it has sufficient energy to ionized atoms or molecules. And recall that ionizing means that they are going to have a charge since electrons are being removed, there's going to be an imbalance of protons and electrons. And so um ionizing radiation because it has penetrative power and lots of energy, it is capable of harming cells directly by destroying molecules within the cells such as D. N. A. And membranes. But it is also capable of creating what are known as reactive oxygen species or R. O. S. And these reactive oxygen species are chemicals that are highly reactive and can lead to damage within the cells themselves. And so sometimes ionizing radiation causes damage directly to cells. And other times the ionizing radiation creates reactive oxygen species. And these reactive oxygen species are chemicals that go on to cause damage inside of the cell. Now the second type of radiation that were briefly going to introduce here is non ionizing radiation. And as its name implies, the non ionizing radiation is not going to be capable of ionizing atoms or molecules. And this is because the non ionizing radiation is going to be less penetrative. It's going to have less penetrated less penetrative power and it's going to have less energy in general. And so uh this non ionizing radiation because it cannot penetrate uh it must be used directly on the microbes themselves and so it cannot go through packaging and things like that. It has to be used directly on the microbes. And so examples of uh non ionizing radiation include UV ultraviolet light and uh ultraviolet light is capable of damaging D. N. A. And proteins in the cell to help kill the microbes and control microbial growth. And also microwaves can actually generate lethal amounts of heat in order to kill microbes. And so if we take a look at our image down below, we can get a better understanding of irradiation which is going to be once again defined as the process of exposing it to radiation. Um And so here we're showing you is the entire electro magnetic spectrum. Uh and so you can see these waves that we're showing you here. Uh They start off really long and the waves get shorter and shorter and shorter and shorter and shorter. The shortest wavelengths have the highest amount of energy and the most penetrative power. And so therefore the higher energy. This is going to be ionizing radiation. And the waves that are longer are going to have less energy and less penetrative power. And so this is going to be the lower energy non ionizing radiation. And so you can see some examples of these different types of radiation down below. Radio waves are going to have really, really long waves. And so they're going to be considered non ionizing radiation here, what we're showing you are microwaves, which once again can generate lethal amounts of heat to kill microbes. But once again, this is a type of non ionizing radiation, visible light is also non ionizing and also so is UV radiation. Ultraviolet light is non ionizing. And then in terms of ionizing radiation we have X rays and gamma rays are all capable of ionizing. Uh And so over here, on the right hand side, we're showing you an image of a laboratory using ultraviolet light UV light to sterilize the laboratory and kill the microbes that might be growing inside of this uh culture hood that you see here inside the laboratory. And then down below, we're showing you an image of two oranges. The left orange is non irradiated, which means that it was not exposed to radiation. And so you can see the microbial growth growing on the surface of this non ionized orange. Uh this non irradiated orange, I should say. And then over here on the right, we're showing you an orange that has been irradiated and notice that there is no microbial growth. And so irradiation can be used to help control microbial growth and help to keep us safe as we use products and eat specific types of foods. And so this here concludes our brief lesson on irradiation as a method to controlling microbial growth. And we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

This method of physical microbial control combines the removal of all moisture with extremely low temperatures.

• A. Desiccation.
• B. Lyophilization.
• C. Irradiation.
• D. Pasteurization.

How does irradiation control microbial growth?

• A. Some types of radiation can create lethal amounts of heat.
• B. Radiation penetrates cells causing damage to DNA and cell membranes.
• C. Radiation creates reactive oxygen species which damage cellular processes.
• D. All of the above are ways that irradiation controls microbial growth.

A heat-sensitive liquid in a laboratory has been contaminated with E. coli bacteria. Which form(s) of microbial growth control could you use to remove this E. coli population from the liquid?

• A. Desiccating the liquid.
• B. Freezing the liquid.
• C. Filtering the liquid.
• D. Boiling the liquid.

How does high pressure processing (HPP) control microbial populations?

• A. Extreme pressure damages the proteins within microbes until they can no longer function.
• B. Extreme pressure destroys DNA and membranes within microbes.
• C. Extreme pressure removes water from microbial cells via sublimation.
• D. Extreme pressure combines with extreme heat to pasteurize the product and kill microbes.