Microbial Resistance and Antimicrobial Action

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Questions and Answers

What is the primary effect of ionizing radiation on microbial cells?

It excites electrons in microbial cells.

It increases the three-dimensional structure of nucleic acids.

It disrupts hydrogen bonding in molecules. (correct)

It creates new covalent bonds in proteins.

Which of the following statements about nonionizing radiation is correct?

It excites electrons without forming new covalent bonds.

It is suitable for disinfecting surfaces of objects. (correct)

It can be used as a sterilizing agent for liquids.

It penetrates deeply into solid materials.

What is a characteristic of phenolic compounds in microbial control?

They have a pleasant odor and are widely preferred.

They are ineffective in the presence of organic matter.

They are highly effective against non-enveloped viruses.

They remain active for extended periods. (correct)

What is the mechanism of action for alcohols in microbial control?

They remove most microbes from skin when swabbed. Signup and view all the answers

Which chemical method of microbial control is known for denaturing proteins?

Halogens Signup and view all the answers

How do oxidizing agents like hydrogen peroxide function in microbial control?

They kill by oxidation of enzymes. Signup and view all the answers

What is the role of surfactants in microbial control?

They disrupt microbial membranes by reducing surface tension. Signup and view all the answers

What potential health risks are associated with the use of certain phenolic compounds?

They are known for their potential carcinogenic effects. Signup and view all the answers

What does the D-value represent in antimicrobial protocols?

The time required to kill 90% of a microorganism population Signup and view all the answers

Which type of germicides are capable of killing all pathogens, including bacterial endospores?

High-level germicides Signup and view all the answers

Which biosafety level involves handling pathogens that do not cause disease in healthy humans?

Biosafety Level 1 (BSL-1) Signup and view all the answers

What is the purpose of autoclaving in microbial sterilization?

To apply pressure and increase boiling temperature Signup and view all the answers

What occurs during the pasteurization process for milk?

Treatment at high temperatures followed by rapid cooling Signup and view all the answers

Which method is considered the ultimate means of microbial sterilization?

Incineration Signup and view all the answers

How does refrigeration affect microbial growth?

It halts growth of most pathogens Signup and view all the answers

What is the effect of lyophilization on microbial cultures?

Allows long-term preservation by preventing ice formation Signup and view all the answers

Which of the following is a disadvantage of using moist heat for sterilization?

Boiling time varies with elevation Signup and view all the answers

What is a characteristic of effective filtration in microbial control?

It sterilizes materials without chemical agents Signup and view all the answers

Study Notes

D-Value

D-value (decimal reduction time) is the time needed for a specific protocol to kill 90% of a microbial population.

Antimicrobial Action

Antimicrobial agents can alter cell membranes, damaging proteins or DNA, causing cell bursting due to osmotic effects.

Factors Affecting Antimicrobial Efficacy

Relative Susceptibility: Microbes vary significantly in their resistance to antimicrobial methods.
- Most resistant: Prions, bacterial endospores, cysts of Cryptosporidium, mycobacteria, cysts of other protozoa, small nonenveloped viruses, active-stage protozoa, fungal spores.
- Less resistant: Most Gram-negative bacteria, vegetative fungi, large nonenveloped viruses, most Gram-positive bacteria, enveloped viruses.
- Most susceptible: (See table above)
Germicide Classification:
- High-level: Kills all pathogens, including endospores.
- Intermediate-level: Kills fungal spores, protozoa cysts, viruses, and pathogenic bacteria.
- Low-level: Kills vegetative bacteria, fungi, protozoa, and some viruses.

Biosafety Levels

Biosafety Level (BSL) 1: Handling pathogens that don't cause disease in healthy humans.
BSL 2: Handling moderately hazardous agents.
BSL 3: Handling microbes in safety cabinets.
BSL 4: Handling microbes causing severe or fatal disease.

Boiling: Kills vegetative bacteria, fungi, and protozoa trophozoites, and many viruses. Boiling times vary with elevation.
Autoclaving: Applying pressure to boiling water prevents steam escape, increasing boiling temperature. Standard conditions: 121°C, 15 psi, 15 minutes.
Pasteurization: Used for milk, yogurt, and juices, not sterilization; heat-tolerant microbes survive. Types include ultrahigh-temperature pasteurization (140°C for 1-3 seconds then rapid cooling).

Used for materials incompatible with moist heat. Denatures proteins, and requires higher temperatures for longer durations. Liquids transfer heat more efficiently. Incineration is ultimate sterilization method.

Refrigeration and Freezing

Reduce microbial metabolism, growth, and reproduction.
Refrigeration halts growth of most pathogens, but not all. Some (like Listeria) can multiply. Slow freezing is more effective than quick freezing. Microbe susceptibility varies.

Desiccation and Lyophilization

Desiccation (drying): Removes water, inhibiting growth.
Lyophilization (freeze-drying): Preserves microbial cultures long-term, avoiding damaging ice crystals (sublimation).

Filtration

Filtration methods remove microbes from a solution by using specific filter pore sizes.

Radiation

Ionizing Radiation: Wavelengths shorter than 1 nm (electron beams, gamma rays, some X-rays). Disrupts hydrogen bonding, oxidizes and creates radicals.
Nonionizing Radiation: Wavelengths greater than 1 nm (UV light). Excites electrons, creates pyrimidine dimers in DNA. Does not penetrate well. Suitable for disinfecting air and surfaces of objects, transparent fluids.

Chemical Methods of Microbial Control

Affect microbes' cell walls, membranes, proteins, and DNA. Effective mechanisms vary across environments. Often more effective against enveloped viruses, vegetative bacteria, fungi, and protozoa.
Phenol and Phenolics: Effective even with organic matter and remain active for a while. Historically used, but potential health risks and unpleasant smell. Recent FDA ruling on some phenols.
Alcohols: Intermediate-level disinfectants; better than soap for removing bacteria from hands; useful in skin-prepping before injections.
Halogens: Intermediate-level antimicrobial chemicals (iodine, chlorine, bromine, fluorine). Denature proteins and interfere with disulfide bonds. Wide-ranging use.
Oxidizing Agents: (hydrogen peroxide, ozone, peracetic acid): High-level disinfectants and antiseptics. Kills via oxidation. Treatment options for drinking water and equipment sterilization.
Surfactants: "Surface-active" chemicals that reduce surface tension (soaps, detergents). Soaps are degerming. Detergents (positively charged) and quats are disinfectants; disrupt membranes.
Heavy Metals: (thimerosal, copper): Heavy metal ions combine with sulfur. Low-level bacteriostatic and fungistatic agents; used in preserving vaccines and controlling algal growth.

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Description

This quiz covers essential concepts related to D-value, antimicrobial action, and the factors affecting the efficacy of antimicrobial agents against various microbes. Test your understanding of microbial resistance classifications and germicide effectiveness through targeted questions.