Chemical Methods to Control Microbial Growth - Online Tutor, Practice Problems & Exam Prep

Chemical methods for controlling microbial growth include sanitizers, disinfectants, antiseptics, and sterilizers. Sanitizers reduce bacteria to meet public health standards, while disinfectants (germicides) target inanimate objects. Antiseptics are safe for living tissues, and sterilizers eliminate all microbes except prions. Disinfectants can be classified as bacteriocides, which kill bacteria, or bacteriostatics, which inhibit growth. Selecting the right chemical agent involves considering its effectiveness against specific microbes, toxicity, storage requirements, cost, and environmental impact, ensuring targeted action without unintended damage.

Chemical Methods to Control Microbial Growth

In this video, we're going to begin our lesson on chemical methods for controlling microbial growth. In addition to the physical methods of controlling microbial growth that we already covered in our previous lesson videos, recall that there are also chemical methods for controlling microbial growth. There are several different types of chemical agents that can be used for controlling microbial growth, including the following four that we have numbered down below. The first is a sanitizer. A sanitizer is a chemical that, as its name implies, is used to sanitize. That means it will be killing mainly bacteria to meet public health standards. Also, recall that sanitization includes the effect of appearing to be clean. Sanitizers also help with the appearance, making the object appear clean.

The next type of chemical agent we have here are disinfectants. Disinfectants are also sometimes referred to as germicides or microbicides. Disinfectants or germicides or microbicides are all synonymous with each other and refer to chemicals that are used to disinfect inanimate or non-living objects. Antiseptics, the third type we have here, is a specific type of disinfectant. However, this type of disinfectant can be safely used on living tissue. Hence, disinfectants are suggested for use on inanimate or nonliving objects, whereas antiseptics are specific types of disinfectants that are safe to be used on living tissues.

Last but not least, we have sterilizers. Sterilizers are chemicals that sterilize by destroying all microbes, of course, except for prions, since those are microbes that are resistant to sterilins. This includes killing off all of the endospores, which are typically resistant to all these other three types. Sterilizers are the only type listed here powerful enough to actually kill endospores.

If you take a look at the image down below, notice at the top we have the sanitizers, which again are used for sanitizing and helping things to appear clean, and they're meeting public health standards allowing you to use sanitizers on your hands right before you eat. Then we have the disinfectants, which, recall, are also sometimes referred to as germicides or microbicides. These are used to disinfect inanimate objects. That means they are going to kill the vast majority of pathogens, but some viable pathogens may still be able to survive. Antiseptics are specific types of different disinfectants that can be used on living tissue. So, if you get a cut or something like that you're able to use antiseptics on your own skin and other living tissues.

Towards the bottom, we have the sterilizers which are going to kill almost all of the living organisms, including all microbes except for prions, and this includes the endospores. This here concludes our brief introduction to the chemical methods of controlling microbial growth. As we move forward in our course, we are going to learn a lot more about different types of chemical methods. I'll see you all in our next video.

Types of Disinfectants

In this video, we're going to talk about the types of disinfectants. Recall from our last lesson video, we said that disinfectants are also sometimes referred to as microbicides or as germicides. These disinfectants are really just chemicals that are used to disinfect inanimate or non-living objects. Now these disinfectants can be grouped based on whether or not they kill or if they inhibit the microbes. They can also be grouped based on the types of microbes that they are most effective against. The suffix -cide is a suffix that means to permanently kill. Thus, bacteriocides are chemicals, disinfectants, that will kill bacteria. Fungicides are disinfectants that kill fungi. You can see how the root bacteria indicates that it kills bacteria and the root "cide" indicates that it is killing these bacteria, and the same goes for the fungicides. The root fungi indicates that fungi are being affected and once again the root "cide" indicates that they are being killed.

On the other hand, the suffix "static" is a suffix that means to reversibly inhibit. That means it can inhibit the growth of those microbes. But, if somehow that disinfectant could be removed, then it could allow for the reversibility and let the microbes continue to grow. For example, bacteriostatics are going to be disinfectants that inhibit bacterial growth. Here again, the bacterial root indicates that bacteria are being affected and the static root suggests that there is inhibition of growth rather than killing. It's important to keep in mind that because their growth is inhibited does not necessarily mean that they are dead. Now, fungistatics will be disinfectants that inhibit fungal growth. The fungi here indicates that fungi are being affected, and the static suffix indicates that there is inhibition of growth rather than killing.

If we take a look at our image below, we can get an even better understanding of the difference between bacteriocides and bacteriostatics. On the left-hand side, we are showing you a bacteriocide. A bacteriocide once again is going to be a disinfectant that will kill bacteria. Notice that we're showing you this plot. On this plot on the y-axis, we have the log of the number of cells. The higher the y value, the more cells there are. The lower the y value, the fewer cells there are. Then on the x-axis, we have the time. Notice initially that there are very few cells, but then these cells start to grow, as they normally would. But notice this particular time point right here is the time for the addition of the bacteriocide. Once the bacteriocide is added, the bacteriocide will begin to kill these cells. Notice that the number of viable cells, the number of living cells, is starting to drop down because those cells are being killed. Also notice that the total number of cells remains the same here after the addition of the bacteriocide. And then notice that even after removal of the bacteriocide, if somehow the bacteriocide were to be removed, those cells have already been killed. Notice that, the cells are not going to continue to grow.

Now notice on the right-hand side we're focusing on bacteriostatics. Bacteriostatics will inhibit the growth of the bacteria rather than kill the bacteria. Notice that we have a similar plot below except notice that with the addition of the bacteriostatic, the number of viable cells remains constant and that the cells are not actually dying off. The number of viable cells remains constant. If it were possible to remove the bacteriostatic, then those viable cells will continue to grow as they were before the addition of the bacteriostatic. This is something important to keep in mind. Once again, bactericides are going to kill the bacteria, permanently kill them, and the bacteriostatics are going to only temporarily inhibit the bacteria until the bacteriostatic is no longer present.

This here concludes our brief lesson on the types of disinfectants, specifically bactericides versus bacteriostatics, 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.

_______________ inhibit the growth of bacteria & ____________________ kill bacteria.

• A. Fungistatics; Fungicides.
• B. Bacteriocides; Bacteriostatics.
• C. Bacteriostatics, Fingicides.
• D. Bacteriostatics, Bacteriocides.
• E. Bacteriocides; Fungistatics.

Selecting the Right Chemical Agent

In this video, we're going to talk about some considerations when selecting the right chemical agent. Selecting a specific chemical agent for controlling microbial growth is actually a really complex process because there are many different things to consider. One of the most important considerations is that the chemical should only target the microbes of interest without causing any unintended damage. It's vital to remember that while the chemical may be effective against the microbe, if it also causes unintended damage, it may not be the best chemical to use for this situation. Below, we have additional considerations for selecting chemical agents for controlling microbial growth:

• The activity of the chemical agent around organic matter: Organic molecules, which contain carbon and hydrogen, are present in all living organisms and can be found in things like soil. Sometimes, if soil is present, the chemical agent, such as bleach, may not effectively perform its function. Therefore, the activity of the chemical around organic matter is a significant consideration for scientists.
• Chemical toxicity: A chemical may be very effective against microbes, but if it is toxic to humans or other forms of life that we do not want to harm, then the chemical may not be suitable. Chemical toxicity is a crucial consideration to ensure we are only targeting the microbes without causing unintended damage.
• Storage capabilities: Some chemicals require very specific types of storage, such as refrigerators or freezers, and others require high pressures or other conditions. The storage capability of the chemical agent can be a limiting factor and can dictate what type of chemical should be used in a scenario.
• The cost of the chemical agent: If a chemical is highly effective against microbes but is also very expensive, it might not be the best option for use. Thus, the cost of the chemical is an important consideration when selecting the chemical agent.
• Environmental impact of the chemical agent: Even if a chemical agent is very effective at controlling microbial growth, if it can act as a pollutant and damage the environment, then it might not be the ideal chemical agent to use.

All these considerations are critical for a scientist in selecting the right chemical agent. Like the physical methods of controlling microbial growth, there is no perfect chemical method that will work in every scenario. Each chemical method has a set of advantages and disadvantages. Scientists must weigh these and make all these considerations to select the appropriate method for the scenario.

This concludes our brief introduction to selecting the right chemical agent, and we will be able to get some practice applying these concepts moving forward in our course. I'll see you all in our next video.