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?

<p>They remove most microbes from skin when swabbed. (C)</p> Signup and view all the answers

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

<p>Halogens (D)</p> Signup and view all the answers

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

<p>They kill by oxidation of enzymes. (B)</p> Signup and view all the answers

What is the role of surfactants in microbial control?

<p>They disrupt microbial membranes by reducing surface tension. (D)</p> Signup and view all the answers

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

<p>They are known for their potential carcinogenic effects. (D)</p> Signup and view all the answers

What does the D-value represent in antimicrobial protocols?

<p>The time required to kill 90% of a microorganism population (B)</p> Signup and view all the answers

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

<p>High-level germicides (B)</p> Signup and view all the answers

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

<p>Biosafety Level 1 (BSL-1) (D)</p> Signup and view all the answers

What is the purpose of autoclaving in microbial sterilization?

<p>To apply pressure and increase boiling temperature (A)</p> Signup and view all the answers

What occurs during the pasteurization process for milk?

<p>Treatment at high temperatures followed by rapid cooling (C)</p> Signup and view all the answers

Which method is considered the ultimate means of microbial sterilization?

<p>Incineration (A)</p> Signup and view all the answers

How does refrigeration affect microbial growth?

<p>It halts growth of most pathogens (C)</p> Signup and view all the answers

What is the effect of lyophilization on microbial cultures?

<p>Allows long-term preservation by preventing ice formation (D)</p> Signup and view all the answers

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

<p>Boiling time varies with elevation (D)</p> Signup and view all the answers

What is a characteristic of effective filtration in microbial control?

<p>It sterilizes materials without chemical agents (C)</p> Signup and view all the answers

Flashcards

D-value

The time needed to kill 90% of a specific microbial population under specific conditions. It's a measure of a microbe's resistance to a particular antimicrobial agent.

Antimicrobial Agent: Alteration of Cell Membranes

Antimicrobial agents can disrupt the cell membrane of microbes, making them leaky. This allows essential molecules to escape and potentially cause the cell to burst.

High-Level Germicide

A powerful germicide that kills all types of microbes, including the most resistant ones like endospores, which are resistant to many disinfectants.

Autoclaving

A sterilization method that uses pressurized steam to kill all microbes, including endospores. It's often used for sterilizing medical equipment.

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Pasteurization

A heat treatment method used to kill harmful microbes in liquids like milk and juice. It doesn't sterilize but significantly reduces the number of microbes.

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Dry Heat Sterilization

Uses high temperatures for longer periods to sterilize materials that can't be treated with moist heat. It's less efficient than moist heat methods.

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Refrigeration and Microbial Growth

Lower temperatures slow down the metabolic processes of microbes, inhibiting their growth and reproduction. However, some microbes can still multiply in refrigerated foods.

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Desiccation

Drying method used to inhibit microbial growth by removing water, a crucial component for their survival.

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Lyophilization

Freeze-drying process used for long-term preservation of microbes. It involves freezing and then removing water through sublimation - ice to vapor.

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Filtration

A physical method used to remove microbes from liquids or gases by passing them through a filter with small pores that trap the microbes.

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What are Phenolics?

Phenolics are a group of antimicrobial chemicals that are effective against a wide range of microbes, even in the presence of organic matter. They remain active for extended periods.

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What are Alcohols used for?

Alcohols are intermediate-level disinfectants that are more effective than soap in removing bacteria from hands. They are often used to swab skin before injections.

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What type of disinfectant are Halogens?

Halogens are intermediate-level antimicrobial chemicals that denature proteins. They are widely used as disinfectants.

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How do Oxidizing Agents kill microbes?

Oxidizing agents like peroxides, ozone, and peracetic acid kill microbes by oxidizing their enzymes.

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What are Surfactants?

Surfactants are surface-active chemicals that reduce the surface tension of solvents. They can be used to remove microbes from surfaces, but are not antimicrobial themselves.

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What is the mechanism of action of Heavy Metals?

Heavy metals like thimerosal and copper combine with sulfur in cysteine, denaturing proteins and inhibiting microbial growth.

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What are the main types of Radiation used for microbial control?

There are two main types: Ionizing radiation, which uses wavelengths shorter than 1nm, and Nonionizing radiation, which uses wavelengths greater than 1nm.

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What are the two types of Radiation control?

Ionizing radiation uses high energy to disrupt microbial DNA and proteins, while Nonionizing radiation excites electrons causing damage to microbial structures.

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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.

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