Micro Bio Chapter 07: Section 7.5-7.6 - The Control of Microbial Growth

A nurse is degerming a patient's arm before giving a vaccination. Which of these concentrations of alcohol is most effective?

70% Two of the most commonly used alcohols are ethanol and isopropanol. The recommended optimum concentration of ethanol is 70%, but concentrations between 60% and 95% seem to kill as well. Pure ethanol is less effective than aqueous solutions (ethanol mixed with water) because denaturation requires water.

Alcohol is most effective when used as a __________ solution.

70% Two of the most commonly used alcohols are ethanol and isopropanol. The recommended optimum concentration of ethanol is 70%, but concentrations between 60% and 95% seem to kill as well. Pure ethanol is less effective than aqueous solutions (ethanol mixed with water) because denaturation requires water.

Which one of the following substances is effective against bacterial endospores?

Chlorine Chlorine (Cl2), as a gas or in combination with other chemicals, is another widely used disinfectant. Its germicidal action is caused by the hypochlorous acid that forms when chlorine is added to water. This chemical is effective against bacterial endospores.

Which one of these halogen compounds would be considered an antiseptic?

Chlorine Dioxide Chlorine dioxide can be used as an antiseptic in low concentrations. Chlorine gas, hypochlorous acid, and calcium hypochlorite are used as disinfectants. Antiseptics are safe to use on living tissues while disinfectants are used to treat non-living surfaces.

Some microbes are very resistant to antimicrobial chemicals. Which of the following would be the easiest to kill?

E. coli E. coli would be the easiest to kill. The cell wall of Mycobacterium tuberculosis and other members of this genus have a waxy, lipid-rich component. The resistance to chemical antimicrobials of members of the genus Pseudomonas is related mostly to the characteristics of their porins (structural openings in the wall of gram-negative bacteria). Porins are highly selective of molecules that they permit to enter the cell. Bacterial endospores are affected by relatively few biocides. The cysts and oocysts of protozoa are also relatively resistant to chemical disinfection.

Which one of these chemical treatments kills cells by causing cross-linking of nucleic acids and proteins and inhibits vital cellular functions?

Ethylene oxide Ethylene oxide kills cells by causing cross-linking of nucleic acids and proteins, which inhibits vital cellular function. This chemical kills all microbes and endospores but requires a lengthy exposure period of several hours. It is toxic and explosive in its pure form, so it is usually mixed with a nonflammable gas, such as carbon dioxide. Among its advantages is that it carries out sterilization at ambient temperatures and it is highly penetrating.

__________ is used to sterilize medical equipment that might be damaged by exposure to the heat of autoclaving.

Ethylene oxide gas

Which one of these products is most useful for disinfecting medical instruments?

Glutaraldehyde Glutaraldehyde is most useful for disinfecting medical instrument, including endoscopes and respiratory therapy equipment. It is a chemical relative of formaldehyde that is less irritating and more effective than formaldehyde. Glutaraldehyde is one of the few liquid chemical disinfectants that can be considered a sterilizing agent.

Which of the following would be the most effective method in preserving bacterial cultures?

Lyophilization In the absence of water, known as desiccation, microorganisms cannot grow or reproduce but can remain viable for years. Then, when water is made available to them, they can resume their growth and division. This is the principle that underlies lyophilization, or freeze-drying, a laboratory process for preserving microbes. Certain foods are also freeze-dried (for example, coffee and some fruit additives for dry cereals).

What is the typical mechanism of action for chemical food preservatives?

Metabolic inhibition The typical mechanism for chemical food preservatives is metabolic inhibition, which will reduce bacterial growth within the food without harming individuals that eat the food.

Which of these chemicals inhibits an enzyme required for synthesis of membrane lipids?

Triclosan Triclosan inhibits an enzyme needed for the biosynthesis of fatty acids (membrane lipids), which mainly affects the integrity of the plasma membrane. It is especially effective against gram-positive bacteria but also works well against yeasts and gram-negative bacteria.

Which of these microbes is the most difficult to destroy using either chemical or physical methods?

Prions Prions are infectious proteins that are the cause of neurological diseases known as spongiform encephalopathies, such as the popularly named mad cow disease. They are the most difficult to destroy using chemical or physical methods. To destroy prions, infected animal carcasses are incinerated. A major problem is the disinfection of surgical instruments exposed to prion contamination. Normal autoclaving has proven to be inadequate and it is now recommended to combine the application of a solution of sodium hydroxide with autoclaving at 134°C.

Which of the following infectious agents challenge the current sterilization strategies that have been accepted and in use for decades?

Prions Prions challenge the current sterilization strategies that have been accepted and in use for decades. Prions are infectious proteins that are the cause of neurological diseases known as spongiform encephalopathies, such as the popularly named mad cow disease. To destroy prions, infected animal carcasses are incinerated. A major problem is the disinfection of surgical instruments exposed to prion contamination. Normal autoclaving has proven to be inadequate and the combined use of a solution of sodium hydroxide and autoclaving at 134°C it is now recommended.

__________ ammonium compounds are less effective against gram-negative bacteria and more effective against gram-positive bacteria.

Quaternary The most widely used surface-active agents are the cationic detergents, especially the quaternary ammonium compounds (quats). Their cleansing ability is related to the positively charged portion, the cation, of the molecule. Their name is derived from the fact that they are modifications of the four-valence ammonium ion, NH4. Quaternary ammonium compounds are strongly bactericidal against gram-positive bacteria and less active against gram-negative bacteria.

__________ has little value as an antiseptic but is important in the mechanical removal of microbes.

Soap Soap and detergent soap has little value as an antiseptic, but it does have an important function in the mechanical removal of microbes through scrubbing. The skin normally contains dead cells, dust, dried sweat, microbes, and oily secretions from oil glands. Soap breaks the oily film into tiny droplets, a process called emulsification, and the water and soap together lift up the emulsified oil and debris and float them away as the lather is washed off. In this sense, soaps are good degerming agents.

Which of the following would most likely resist dessication and high pressure?

Spore-forming bacteria In the absence of water, known as desiccation, microorganisms cannot grow or reproduce but can remain viable for years. Then, when water is made available to them, they can resume their growth and division. This is the principle that underlies lyophilization, or freeze-drying, a laboratory process for preserving microbes. Spore-forming bacteria would most likely resist desiccation and high pressure.

A nurse is working in southeast Asia, where the incidence of Mycobacterium tuberculosis is very high. Why is it necessary to select a specific method of disinfection for this organism?

The waxy, lipid-rich components of the cell wall make this organism relatively resistant to disinfectants. It is necessary to select a specific method of disinfection for this organism because the waxy, lipid-rich components of the cell wall make this organism relatively resistant to disinfectants. The cell wall of Mycobacterium tuberculosis and other members of this genus have a waxy, lipid-rich component. Instruction labels on disinfectants often state whether they are tuberculocidal, indicating that they are effective against mycobacteria. Special tuberculocidal tests have been developed to evaluate the effectiveness of biocides against this bacterial group.

__________ is a compound found in antimicrobial soaps that targets gram-positive bacteria.

Triclosan A widely used bisphenol is triclosan, an ingredient in antibacterial soaps and at least one toothpaste. Triclosan inhibits an enzyme needed for the biosynthesis of fatty acids (lipids), which mainly affects the integrity of the plasma membrane. It is especially effective against gram-positive bacteria but also works well against yeasts and gram-negative bacteria. Its use is now so widespread that resistant bacteria have been reported, and concerns about its effect on microbes' resistance to certain antibiotics have been raised.

The following may be listed on the ingredient list of your favorite snack food. Which of these products is NOT antimicrobial? Xanthan Calcium propionate Potassium sorbate Sorbic acid Sodium benzoate

Xanthan Xanthan is NOT an antimicrobial. It is a microbial product used as a thickening agent.

All of the following are examples of microbial control using heavy metals EXCEPT __________. benzoyl peroxide used for acne treatment burn treatment using silver-sulfadiazine ointment algae control in swimming pools using copper sulfate mouthwash solution containing zinc chloride antiseptic solution containing mercurochrome

benzoyl peroxide used for acne treatment Benzoyl peroxide used for acne treatment is NOT an example of microbial control using heavy metals. Benzoyl peroxide, which is probably most familiar as the main ingredient in over-the-counter medications for acne is an oxidizing agent.

Oxidizing agents, such as hydrogen peroxide, are useful for irrigating deep wounds, in which released oxygen will inhibit the growth of __________.

obligate anaerobes Oxidizing agents, such as hydrogen peroxide, are useful for irrigating deep wounds, in which released oxygen will inhibit the growth of obligate anaerobes. Oxidizing agents, such as hydrogen peroxide, are useful for irrigating deep wounds, in which released oxygen will inhibit the growth of anaerobic bacteria. The released oxygen is toxic to anaerobes, which will be killed in its presence.

Recently, silver has been considered in new applications for microbial control, such as impregnating surgical dressings and infusing food containers with silver. These new applications are important because silver is __________.

oligodynamic and unaffected by antimicrobial resistance Recently, silver has been considered in new applications for microbial control, such as impregnating surgical dressings and infusing food containers with silver. These new applications are important because silver is oligodynamic (oligo means "few") and unaffected by antimicrobial resistance. This action can also be seen when we place a coin or other clean piece of metal containing silver or copper on a culture on an inoculated Petri plate. Extremely small amounts of metal diffuse from the coin and inhibit the growth of bacteria for some distance around the coin. This effect is produced by the action of heavy metal ions on microbes. When the metal ions combine with the sulfhydryl groups on cellular proteins, denaturation results.

An antiseptic is used to remove microbes from __________.

skin, before an injection The chemical used to remove microbes from skin, before an injection, is called antiseptic. The term used for the treatment is called "antisepsis."