Selecting a Method to Control Microbial Growth

in this video, we're going to begin our lesson on selecting a method to control microbial growth. And so selecting an effective method to control microbial growth is actually a really challenging process. And this is not only because there are a ton of microbial growth control methods, but also because each individual method has a set of advantages and a set of disadvantages. And so really what this means is that a perfect microbial growth control method does not exist. There's not a single microbial growth control method that will work in every single scenario. And this is once again because each individual method has a set of advantages and also a set of disadvantages as well. And so in order to select an appropriate uh microbial growth control method, there are some important considerations that should be made. And notice that we're listening these five important considerations in this table down below. And so notice our scientists over here is asking, hmm, what method of microbial growth control should I be using. And in order to answer that question, you should make these five considerations that we have down below. The first consideration is simply the types of microbes that are present. And recall that different types of microbes can have different microbial characteristics. And so by knowing the microbial characteristic and the type of microbes that can help dictate what methods are going to be useful and what methods may not be useful. And that's because sometimes some microbial growth control methods will work for one type of microbe, but they will not work for a different type of microbe. And we'll be able to talk more about this specific idea and each of these considerations in more detail as we move forward in our course. Now, the second consideration that should be made, It's not only the type of microbe but also the number of microbes, how many microbes are there? If there are a lot of microbes then that may require a different control method than if there were only a little bit of the microbes. So that is also an important consideration. Another important consideration is this 3rd 1 here, which is the overall risk of infection. Uh and so if there is a low risk of infection or of a human being infected, then uh that may change the the microbial growth method that is used. Um And if there is a high risk of infection then that may also dictate the microbial growth control method that is used. The next consideration that's also important to take into account is environmental factors. For example, the temperature and the ph can all impact the effectiveness of a microbial growth control method. And last but not least. The last consideration that should be made when selecting microbial growth control method is the composition of the item that is going to be treated for microbes and so whether the uh the item that is being treated is made out of glass or plastic can actually matter. And so that is another consideration that is important to take into account. And so once again we're going to talk about each of these five considerations and more detail as we move forward in our course. But for now this year concludes our brief introduction to selecting a method to control microbial growth and the considerations that should be made before or while selecting a control microbial growth method. And so I'll see you all in our next video to talk even more about each of these considerations.

in this video, we're going to talk more about the first consideration to be made when selecting a microbial growth control method and that is the types of microbes and the microbial characteristics that are present. And so once again, the types of microbes, along with the microbial characteristics, are going to be really important considerations when selecting a microbial growth control method. And so this is because some microbes are actually really, really highly resistant to particular microbial growth control treatments, meaning that they will not die by a specific control method, whereas other microbes may be sensitive to the same exact treatment method, meaning that they will die in the presence of that treatment method. And so the type of microbe is going to be a very important consideration because it can help dictate whether a disinfection method can be used, or whether a more powerful sterilization procedure should be used. And so, if we take a look at this image down below, on the left hand side, we can get a better understanding of how different types of microbes can have different resistance levels to particular control methods. And so notice that on the far left hand side over here uh left hand column uh this is a column showing you different types of microbes. And notice that these different types of microbes are arranged based on their resistance to particular microbial control methods. So notice the ones that are towards the top with the whitish background are going to be less resistant and that means that they are going to be more susceptible, meaning that they will die rather easily by a microbial growth control method. And as you start to go downwards towards the bottom um the microbes start to become more and more resistant. And of course being resistant means that they are able to survive in the presence of that method and so on. The far right, what we're showing you as a column of the microbial control method that's uh going to be uh sufficient enough to uh basically control the particular microbe. And so notice that for enveloped viruses such as the SARS Kobe to virus that causes Covid 19 HIV and hepatitis B viruses um enveloped viruses are not very resistant. Okay they're very susceptible. And so really low level disinfection control methods are going to be suitable for dealing with enveloped viruses and also for dealing with most vegetative bacteria such as for example s arias and end gonorrhea. Um Now notice that fun guy and non enveloped viruses uh start to become more a little bit more resistant. And so they require high level disinfection methods in order to control these microbes. And um you can see some examples of fun guys such as ringworm and athlete's foot and also non enveloped viruses. Examples are poliovirus or polio and rhinovirus which is responsible for the common cold. Uh then noticed that mycobacterium and bacterial endo spores are even more resistant. And so they require more powerful sterilization techniques. And so if we were to use a low level disinfection technique on one of these uh microbes here, mycobacterium or bacterial spores, it would not be sufficient to control them. And so only sterilization procedures are going to be sufficient for these microbes and then towards the very very bottom what we have our pry ins and recall that cry ins are going to be very um difficult to control. And so it requires even more powerful control methods than sterilization. Such as for example pry on elimination techniques. And so those are the most resistant microbes are the prions. And so basically the big takeaway that you can get from this image is that the type of microbe really does matter because whether we're dealing with enveloped viruses or whether we're dealing with bacterial endo scores, it really matters because it will dictate what type of control method is going to be suitable and uh lower level disinfection methods will not be suitable uh to basically handle more resistant forms or more resistant types of microbes. Now over here on the far right. What we're showing you is a graph that is showing you the time for sterilization basically how long it takes to kill a particular microbe. And so notice on the Y. Axis it's showing the log of the number of viable cells basically showing you how many viable cells there are, how many living cells there are. The higher the Y. Value the more living cells, the lower the Y. Value the less living cells the more dead cells there are and so on the X. Axis. What we have is the time progressing from left to right. And so notice that we have two different curves on, we have two different lines on this graph. We have this yellow line right here and then we have this orangish line right here and notice that the yellow line represents vegetative bacterial cells. Whereas this orangish line right here represents endo spores and recall from our previous lesson videos and from this table over here uh that endo spores are fairly resistant and they require more stringent um control methods whereas vegetative bacteria are up here and they are less resistant, more susceptible. And so notice that the vegetative bacteria are able to be killed or sterilized in a less amount of time. Whereas the end of spores require a lot more time in order to be completely sterilized and completely killed off. And so once again, this is just showing you how that the time that's required for sterilization sterilization actually depends on the type of microbe that is present. And so all of this is just to emphasize the fact that the types of microbes that are present is a really important consideration when selecting the microbial growth control method. And so this year concludes our brief lesson on this idea here and we'll be able to learn more about the other considerations and apply these concepts here as we move forward. So I'll see you all in our next video.

Which of the following questions are important to answer before attempting to control a microbial population?

• A. What type of microbe am I trying to control?
• B. What kind of environment is the microbe in?
• C. What is the size of the microbial population?
• D. All are important questions to answer.

Which microbe has the highest level of resistance to control methods that humans currently possess?

• A. Mycobacteria (bacteria that cause tuberculosis).
• B. Enveloped viruses (Covid-19 virus, HIV, etc.).
• C. Prions.
• D. Bacterial endospores.

in this video, we're going to talk about the second consideration when selecting a method for microbial growth control and that is the number of microbes that are present. And so when a microbial population is treated with either a physical or a chemical process, usually the microbes within that microbial population die at a constant great Rather than dying all at one single time. And so what this means is that the larger the population of microbes is initially, the longer it's going to take for uh the entire population to be destroyed. And so washing and scrubbing can help to remove microbes and biofilms, and ultimately it reduces the time to sterilize or disinfectant item. If you are able to get rid of some of the microbes that are present just by physical destruction, by washing and scrubbing. Um Now down below, we're showing you these two plots, this one and this one over here, and these are what are known as microbial death curves. And so microbial death curve is a plot of the death of a microbial population over time due to either a physical or a chemical microbial control treatment method. Now on these plots, but you're going to find is a value known as the decimal reduction time, or just the D value for short. And so the decimal reduction time or the D value is really just referring to the specific amount of time that's required to kill 90% of the microbial population under set conditions. And what's important to note here is that the greater the D value is, the more resistant the microbial population is to the specific treatment method. And so if we take a look at our image down below, we can get a better understanding of this decimal reduction time or devalue along with how the number of microbes can impact the type of uh method that should be used. And so over here on the left we're showing you once again a microbial death curve along with the D. Value. And so notice on the Y axis we have the number of living microbial cells and on the X. Axis we have the amount of time in minutes. And so notice that initially at time zero we're starting with a population of 10,000 microbes and noticed that when applying this particular microbial growth control method that the population starts to decrease over time. And notice that when 90% of the population is missing, notice going from 10,000 cells down to 1000 cells, that's a 90% drop off there. So this is a log arrhythmic scale y axis. And so this is the population after one devalue. And so what you can see is that uh The d. value once again is going to be the amount of time that it takes for 90% of the population to die. and so from 10,000 down to 1000, that means 9000 cells have died at this point and that is 90% of the population has been killed. And so that corresponds with five minutes. And so the D. Value is represented by this chunk of time here, it's five minutes for this particular plot. Now the next point that you see here represents the population after two devalues. Uh So if the D. Value is five minutes to devalues is 10 minutes and at this point here, what we have is the population after three D. Values, which would be 15 minutes and so on. And so it takes four D. Values for this particular plot here Which is 20 minutes in order to kill off the entire population. And so once again the d. value just represents the amount of time required to kill 90% of the microbial population. And in this particular plot the d. value is five minutes. And so notice that every five minutes 90% of the population is going to be killed. And so it does take 20 minutes to kill off a population of 10,000 cells. If the d. value is five minutes now, over here on the right microbial death curve, we're showing you a similar plot. The number of microbial, the number of living microbial cells on the Y axis, the amount of time on the X. Axis. But this time noticed that we are implementing two different microbial growth control methods. Um A. Is going to be radiation and B. Is going to be sodium hypochlorite or bleach. And so A. Is of course going to be um the yellow line that goes downwards like this and be is going to of course be this line that goes like this. And so what you'll notice is that these two different lines have different devalues or decimal reduction times. Um for a notice that to go from 10, cells to 1000 cells, a 90% reduction. Uh the the value is five minutes just as we saw over here on the left hand side. But notice that for kurt for the line B to go from 10,000 to 1000 cells right here, It is actually a 10 minute devalue. And so here we can add that in. And so basically what we're showing you here is that it takes a lot more time 40 minutes to kill off the entire microbial population using sodium hypochlorite. However, it takes half the amount of time to kill the microbial population using radiation. And so radiation is a more effective means of killing the microbial population because you can kill the microbial population in less time. And so essentially what we're saying is that the greater devalue, greater devalues correspond with microbes that are more resistant. Uh And if there are more resistant to the chosen method, then of course that means that it's going to take them longer uh to die off. And so the microbes are more resistant to sodium hypochlorite than they are to radiation. And that's what this plot is showing. And so ultimately what we're saying here is that the number of microbes is going to impact the microbial control method, because it can dictate the amount of time uh that these uh microbial populations need to be exposed to the treatment. And so this year concludes our lesson on this idea here, and we'll be able to get some practice applying these concepts, and talk more about the other considerations for selecting a microbial growth control method as we move forward in our course, So I'll see you all in our next video.

The decimal reduction time refers to the amount of time it takes to which of the following?

• A. Reduce a microbial population by 10%.
• B. Reduce a microbial population by 0.1%.
• C. Reduce a microbial population by 90%.
• D. Completely eliminate a microbial population.

Which microbial control method is most effective for killing a population of Bacteria X?

• A. A microbial control method with a D-value of 1 hour.
• B. A microbial control method with a D-value of 10 minutes.
• C. A microbial control method with a D-value of 30 minutes.
• D. A microbial control method with a D-value of 2 hours.

in this video, we're going to talk about the third consideration when selecting a microbial growth control method and that is the overall risk of infection that the item being treated presents. And so once again the risk of infection that a particular item presents is going to dictate the method of controlling microbial growth. That's going to be used. Now. Medical instruments and tools are actually categorised into three groups based on the risk of infecting a patient. And so we've got those three groups numbered down below. And we've also got images of these three groups down below in the image. Now, the first group is actually going to be the non critical instruments. And as their name implies, these are going to be medical instruments and tools that present a really low risk of infection, a really low risk of infecting the patient. And that's usually because these items only make contact with the skin of on the outside of a patient. And so these items only uh need to be treated with low level disinfectants because they present a low risk of infection. And so if we take a look at our image down below, at the overall risk of infection in these three groups over here on the far left, we have the non critical instruments which once again present a really low risk of infection. And they're going to usually make contact only with this skin of the patient. And so they do not penetrate into the tissues or anything like that. And so the items such as stethoscopes, which measure heart rate and crutches, which can help you walk around if you have an injured foot. And even items like blood pressure cuffs are all examples of non critical medical instruments that present a low risk of infection. And so only low level disinfection is required for these low risk non critical instruments. Now the next group that we have are these semi critical instruments. And semi is a route that means partially critical. And so as their name implies, these are these instruments are going to present a medium a medium risk of infection or a medium risk of infecting the patient. And so these require higher level disinfection methods and so they're going to be more powerful because the instrument has a greater risk of infecting the patient. And so if we take a look at our image down below notice the semi critical instruments are right here in the middle and these once again present a medium risk of infection to the patient. And so this could um examples of instruments that are going to be semi critical include endoscopes which are basically these scopes that can go into the gastrointestinal tract of a human. So they're going into the body but they're not actually penetrating into any tissues. And so they do present a medium risk of infection. And then of course, last but not least what we have are the critical instruments and critical instruments, as their name implies, they present a really high risk of infection or really high risk of infecting the patient. And so therefore these critical instruments must be sterile in order for them to be used appropriately in a medical setting. And so if we take a look at our image down below at the critical instruments, once again, these present a really high risk of infection. And so these are gonna be instruments such as surgical instruments that are going to penetrate into the tissue of the patient. And so they need to be sterile, which means that no living microorganisms are going to be present on. And so this here concludes our lesson on how the overall risk of infection is an important consideration when selecting the microbial growth control method and once again, depending on if it's a low risk of infection, a medium risk of infection or high risk of infection, um that might dictate whether low level disinfection methods, high level disinfection methods or sterilization methods are required for that particular item that's going to be treated, and so we'll be able to get some practice applying these concepts here as we move forward. But for now, I'll see you on our next video.

in this video, we're going to talk about the fourth consideration when selecting a microbial growth control method and that is environmental factors. And so environmental factors such as the temperature for example and the P. H. Can actually influence the effectiveness of a microbial growth control method. And so for example if the temperature or the ph ranges are not correct within the appropriate range, then the microbial growth control method may be ineffective, meaning that it may not work as it is supposed to or intended to. And on top of environmental factors such as temperature and ph other environmental factors such as substances including grease and dirt and body fluids can actually interfere with some microbial growth control methods, and therefore these items here should be cleaned out appropriately prior to implementing any disinfection or sterilization control methods. And so if we take a look at our image down below, we can get a better understanding of how environmental factors can actually affect microbial growth control methods. And so once again we're showing you a microbial death curve, but with the use of sodium hypochlorite as a chemical microbial growth control method. And so notice on the Y axis we have the number of living microbial cells and on the X axis we have the amount of time that these cells have been exposed to the microbial growth control method. And so notice that we have these two lines here, we have this one here in orange and then we have this one here in blue and the one in orange represents a hot temperature Of of 55°C and the one in blue represents a cold temperature of 50°C. And so notice that there's only a 5°C difference, which you might think might not make a difference in um the control method. However, in this particular example it does make a really big difference. And so what you'll notice is that for the hotter temperatures, the d value um is much smaller and the d value is the decimal reduction time, the amount of time it takes to kill 90% of the population and that percent. Uh that devalue is actually a value of 10 here for the orange curve here, it takes 10 minutes to kill 90% of the population. Notice that both um lines here are starting with the initial population of 10,000 and to go from 10,000 to 1000, which is 90% killed. It takes 10 minutes for this orange curve. And so the hotter temperature is going to be more effective than the colder temperature because notice that the D value for the colder temperature is actually double and so it's a greater devalue and that shows that these microbes are more resistant to colder temperatures. And so it takes a lot longer to kill all of the microbes um when the temperature is colder and it takes a lot less time to kill all of the microbes when the temperature is hotter. And so this is all just emphasizing the fact that household bleach is more effective at killing microbes at hot temperatures, specifically temperatures of 55°C. And so this shows that even small temperature changes like 5°C can actually have a major impact on the microbial growth control method. And so this is why environmental factors are an important consideration when selecting the microbial growth control method. And so this year concludes our lesson on this idea and we'll be able to get some more practice and talk about the fifth and final consideration of selecting a microbial growth control method in our next video. So I'll see you all there.

Match the type of instrument with its correct level of microbial infection risk.

• A. Critical Instruments:High risk.
• B. Non-Critical Instruments:Medium risk.
• C. Semi-Critical Instruments:Low risk.
• D. All are matched correctly.

What can affect the effectiveness of a microbial growth control method?

• A. The temperature of the environment the control method is being used in.
• B. The pH of the environment the control method is being used in.
• C. The presence of grease, dirt, or body fluids on the surface contaminated with microbes.
• D. The type of microbe you are trying to control.
• E. All of the above.

In this video, we're going to talk about the fifth consideration when selecting a microbial growth control method and that is the composition of the item to be treated. And so some physical and chemical processes that control microbial growth are actually inappropriate for certain types of material. And so some physical methods like heat and irradiation can actually cause damage to some types of plastics. And so that is a consideration that needs to be made. Also, liquid chemical disinfectants can also cause damage to certain types of materials, such as electrical equipment, for example. And so all that we're trying to say here is that the composition of the item to be treated has to be compatible with the microbial growth control method. And so depending on the material or the composition of the item that will dictate what microbial growth control method can be used. And so if we take a look at the left hand side over here and notice that we have this plate or this dish here, that's made of plastic and this plastic plate actually melted from having excessive heat. And so although the heat may have killed the microbes, it also damaged the plastic. And now this dish is no longer usable. And so that would not be the best microbial control method for this type of plastic material. And over here on the right, what we're showing you is some electrical equipment. And of course, liquids are going to damage most electric electronic, most electronic equipment, most electrical equipment. So liquids are not going to be compatible with electrical equipment. And so perhaps another type of methods, such as a gas or something like that could be used as a replacement. And so this year concludes our brief lesson on this fifth consideration the composition of the item to be treated when selecting a microbial growth control method. And so 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

Why must the composition of the item being treated be compatible with the microbial growth control method?

• A. If the item and the control method are not compatible then the microbes will die faster.
• B. If the item and the control method are not compatible then the item can be damaged by the control method.
• C. If the item and the control method are not compatible then the control method will be ineffective.
• D. None of the above.