Microbiology Chapter 11: Microbial Control Methods

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Questions and Answers

What is a consequence of blocking cell wall synthesis?

The cell becomes fragile and is lysed easily (correct)

The cell becomes resistant to antibiotics

The cell increases nutrient absorption

The cell can divide normally

How do surfactants affect the cell membrane?

They increase cellular energy production

They enhance protein function

They insert and disrupt the lipid bilayer (correct)

They strengthen the lipid bilayer

Which agent binds irreversibly to DNA and prevents transcription?

Ultraviolet light

Gamma radiation

Formaldehyde (correct)

Chloramphenicol

What happens when proteins are denatured by agents?

They undergo complete unfolding Signup and view all the answers

What is the correct definition of thermal death time?

The time taken to kill all microbes at a specific temperature Signup and view all the answers

Which of the following is NOT a method of moist heat control?

Incineration Signup and view all the answers

Which type of radiation is considered a method of controlling microorganisms?

Gamma radiation Signup and view all the answers

What is one advantage of using filtration for microbial control?

It removes particles without altering product composition Signup and view all the answers

What is the primary purpose of using elevated temperatures in microbial control?

To achieve microbial lethality Signup and view all the answers

What is Thermal Death Time (TDT)?

The shortest length of time to kill all test microbes at a certain temperature Signup and view all the answers

Which method does not achieve sterilization?

Boiling water Signup and view all the answers

What is the most efficient pressure-temperature combination for sterilization using an autoclave?

15 psi at 121°C Signup and view all the answers

Which pasteurization method involves exposing liquids to 71.6°C for 15 seconds?

Flash method Signup and view all the answers

What characterizes nonpressurized steam method (tyndallization)?

Repeated exposure and incubation over several days Signup and view all the answers

What primarily distinguishes incineration from other heat methods of microbial control?

It aspires to achieve complete microbial reduction Signup and view all the answers

Which of the following statements about the boiling water method is true?

It is considered a disinfection method. Signup and view all the answers

What is the primary function of a dry oven in microbial control?

To utilize high temperatures for heat-resistant items Signup and view all the answers

What process involves the dehydration of vegetative cells when exposed to air?

Desiccation Signup and view all the answers

Which type of radiation is known for penetrating solid barriers and causing significant cellular damage?

X rays Signup and view all the answers

What is the main outcome of nonionizing radiation on DNA?

Formation of abnormal bonds leading to mutations Signup and view all the answers

How does cold temperature affect microbial growth during food processing?

It slows down the growth of cultures and microbes Signup and view all the answers

What is lyophilization mainly used for?

Preservation of microorganisms in a viable state Signup and view all the answers

What distinguishes ionizing radiation from nonionizing radiation?

Ionizing radiation ejects electrons from atoms Signup and view all the answers

Which of the following statements about cold and freezing is true?

Freezing preserves microbial cultures effectively Signup and view all the answers

What is one advantage of using filtration in beverage processing?

It can decontaminate beverages without altering their flavor Signup and view all the answers

Which of the following is NOT a factor that affects the germicidal activity of chemicals?

Temperature of the environment Signup and view all the answers

What is a characteristic of a suitable microbicidal chemical?

It should have rapid action even in low concentrations Signup and view all the answers

Which of the following is a common application of HEPA filters?

Removing airborne contaminants Signup and view all the answers

Which category of germicidal agents does NOT include alcoholic compounds?

Detergents Signup and view all the answers

What is one of the main concerns when choosing a microbicidal chemical for health care use?

It should be affordable and readily available Signup and view all the answers

What type of filtration method is suitable for preparing heat-sensitive liquids?

Membrane filtration Signup and view all the answers

How many different antimicrobial chemical agents are approximately manufactured?

10,000 Signup and view all the answers

What does sanitization specifically aim to achieve?

Mechanically remove microorganisms to safe levels Signup and view all the answers

Which factor does NOT affect the death rate of microorganisms when using antimicrobial agents?

Color of the agent Signup and view all the answers

What is the definition of degermation in the context of microbial control?

Reduction of microbial numbers on human skin Signup and view all the answers

To achieve sterilization, what is the vital criterion regarding the population of microbes?

The number of survivors must be infinitesimally small Signup and view all the answers

Which of the following is NOT considered when selecting a microbial control method?

The brand reputation of the antimicrobial agent Signup and view all the answers

Which statement accurately describes microbicidal agents?

They cause irreversible damage to microbial cells. Signup and view all the answers

How is the effectiveness of an antimicrobial agent primarily influenced?

By a combination of factors including microbial load and concentration Signup and view all the answers

What is one of the main actions of antimicrobial agents on the cell wall of microorganisms?

They block the synthesis of the cell wall. Signup and view all the answers

What is the primary goal of sterilization?

To destroy all microbial life, including viruses Signup and view all the answers

Which of the following best describes the process of antisepsis?

Application of antiseptics to living tissues Signup and view all the answers

Which of the following microbial forms is considered most resistant to control measures?

Bacterial endospores Signup and view all the answers

What type of agent is a bactericide?

An agent that destroys bacteria, but not spores Signup and view all the answers

How does disinfection differ from sterilization?

Disinfection does not eliminate bacterial endospores, sterilization does Signup and view all the answers

Which statement accurately describes decontamination?

It decreases the risk of infection without needing full sterilization Signup and view all the answers

What characterizes a microbistatic agent?

It inhibits the growth of microorganisms Signup and view all the answers

Which of the following is an example of a typical disinfectant?

5% bleach solution Signup and view all the answers

Which type of microbial control method prevents the growth of fungi?

Fungistatic agent Signup and view all the answers

Study Notes

Microbiology: A Systems Approach, 2nd ed.

Chapter 11 covers Physical and Chemical Control of Microbes.

Controlling Microorganisms

Distinguishing between sterilization, disinfection, antisepsis, and decontamination is crucial.
Sterilization destroys all microbial life.
Disinfection destroys most microbial life, reducing contamination on inanimate surfaces.
Antisepsis destroys most microbial life, reducing contamination on living surfaces.
Decontamination is the mechanical removal of most microbes from inanimate or animate surfaces.

Microbial Control Methods

Physical agents include heat (dry and moist), radiation (ionizing and nonionizing), and filtration.
Chemical agents include various compounds, categorized by their mechanism of action.
Mechanical methods include filtration, removing microbes

Relative Resistance of Microbial Forms

Endospores are the most resistant microbial forms, followed by other forms.
The goal for bacterial vegetative cells and endospores is sterilization.
The resistance of different microbial forms varies, impacting the control methods needed.

Terminology and Methods of Microbial Control

Sterilization removes all viable microorganisms, including viruses.
Sterile materials are usually inanimate objects, often relying on heat.

Disinfection

Disinfection uses a physical method or chemical agent to destroy vegetative pathogens.
Disinfection does not kill endospores.
It's used on inanimate objects and also removes toxins.

Antisepsis

Antiseptics are used directly on exposed body surfaces.
Sepsis is the growth of microorganisms in the blood and other tissues.
Asepsis is any practice that prevents infectious agents from entering sterile tissues.

The Agents Versus the Processes

Germicides kill microorganisms.
Bactericide kills bacteria.
Fungicide kills fungal spores, hyphae, and yeasts.
Virucide inactivates viruses.
Sporicides kill endospores.
Germicide and microbicide kill microorganisms.
Stasis is preventing the growth of microorganisms.
Bacteristatic prevents bacteria growth.
Fungistatic inhibits fungal growth
Microbistatic materials control microorganisms in the body.

Decontamination

Decontamination reduces the risk of infection or spoilage (e.g. food industry).
Sanitization mechanically removes microorganisms to reduce contamination to safe levels.
Sanitizer is usually a compound like soap or detergent.
Sanitation does not always ensure that no microbes remain but is safe for normal use.
Degermation reduces the number of microbes on human skin (e.g., alcohol wipes).

Practical Concerns in Microbial Control

Sterilization or disinfection may be needed based on the application.
Reusability of items should be considered, along with their ability to withstand processes like heat, pressure, radiation, or chemicals.
Controlling factors such as application suitability, agent penetration, cost- and labor-effectiveness, and safety are all important.

What is Microbial Death?

Microbial death occurs when cell structures become dysfunctional and irreversible damage ensues.
If a cell cannot reproduce under ideal conditions, it's considered dead.

Factors That Affect Death Rate

The length of exposure, load of microbes, relative resistance of spores versus vegetative forms and the action of the agent are all factors impacting death rates.

Factors That Influence the Action of Antimicrobial Agents

The number of microorganisms, the nature of the microorganisms, the temperature and pH of the environment, the concentration of the agent, the mode of action of the agent, the presence of solvents, interfering organic matter, and inhibitors.

How Antimicrobial Agents Work: Their Modes of Action

Agents can affect cell walls (blocking synthesis, digesting or breaking down the surface, leading to cell lysis).
Cell membrane disruptions are possible with agents.
Agents can affect cellular synthetic processes and proteins.

Methods of Physical Control

Six methods of physical control are named and described, along with examples of each method's use.
Moist and dry heat methods are compared and contrasted.

Heat as an Agent of Microbial Control

Elevated temperatures are microbicidal.
Lower temperatures are microbistatic.
Moist and dry heat can both be used.

Comparison of Times and Temperatures to Achieve Sterilization with Moist and Dry Heat

Providing a table of temperatures and times for moist and dry heat methods of microbial control

Practical Concerns in the Use of Heat: Thermal Death Measurements

Temperature and exposure length must be considered.
Higher temperatures generally allow for shorter times.
Lower temperatures require longer exposure times.
Thermal death time (TDT): the shortest time to kill all microbes at a given temperature.
Thermal death point (TDP): the lowest temperature needed to kill all microbes in a sample in 10 minutes.

Common Methods of Moist Heat Control

Methods of moist heat control are detailed (steam under pressure, non-pressurized steam, pasteurization, and boiling water).

Steam under pressure

Pressure raises the temperature of steam allowing for a highly effective sterilization method (Autoclave).
15 psi yields 121°C.

Nonpressurized Steam

Also known as intermittent sterilization or tyndallization, using intermittent heating cycles with incubation periods between exposures.

Pasteurization

Used to disinfect beverages and fluids.
Special heat exchangers used for both flash and batch methods.
Does not kill endospores or thermoduric microbes.

Boiling Water

Used for disinfection, not sterilization.
Expose materials to boiling water for 30 minutes.

Dry Heat: Hot Air and Incineration

Incineration reduces microbes to ashes and gas.
Burning inoculating loops and needles is a common practice.
Tabletop infrared incinerators are also used.

Dry Oven

Electric oven where coils radiate heat within an enclosed compartment.
Exposure to 150-180°C for 2-4 hours.
Often used with heat-resistant items that don't sterilize well by moist heat method.

The Effects of Cold and Desiccation

Cold slows growth but does not kill most microbes; freezing preserves cultures.
Desiccation dehydrates vegetative cells with direct exposure to room air.
Lyophilization (freeze-drying) preserves microorganisms for many years.

Radiation as a Microbial Control Agent

Radiation is high-velocity energy from atomic activities.
Gamma rays, X rays, and UV radiation are used for microbial control.

Modes of Action of Ionizing Versus Nonionizing Radiation

Ionizing radiation ejects orbital electrons, forming ions and causing damage.
Nonionizing radiation excites atoms to higher states but does not ionize them.

Ionizing Radiation: Gamma Rays, X Rays, and Cathode Rays

Cold sterilization using gamma rays, X rays, and cathode rays.
Dosage is measured in Grays.
Exposure ranges from 5 to 50 kiloGrays.
Penetration power differs between types

Applications of Ionizing Radiation

Used in food and medical products.

Nonionizing Radiation: Ultraviolet Rays

Wavelength approximately 100-400 nm.
Germicidal lamp using 254 nm radiation.
Not as penetrating as ionizing radiation.

Applications of Ultraviolet Radiation

Disinfects hospital rooms, operating rooms, schools, food prep areas, and dental offices.
Used to treat drinking water or purify liquids (a type of disinfection).

Decontamination by Filtration

Filtering fluids removes microbes with small openings (pores).
Cellulose acetate, polycarbonate, and plastic types are commonly used.

Applications of Filtration

Used for liquids that can't withstand heat.
Decontaminates beverages.
Purifies water, removes airborne contaminants (HEPA filters).

Chemical Agents in Microbial Control

Approximately 10,000 antimicrobial chemical agents are manufactured.
Approximately 1,000 are routinely used (usually in liquid, gaseous, or solid state).

Choosing a Microbicidal Chemical

Choosing a chemical agent depends on characteristics such as rapid action, stability, broad spectrum, non-toxicity, penetration, resistance to inactivation, non-corrosion, sanitizing/deodorizing properties and affordability.

Factors That Affect the Germicidal Activity of Chemicals

The nature of microorganisms, the nature of the material, the degree of contamination, the time of exposure, and the strength of the germicide.

Required Concentrations and Times for Chemical Destruction of Selected Microbes

Table with required concentrations and times for the disinfection/sterilization of specified microbes.

Qualities of Chemical Agents Used in Health Care

Table providing qualities of chemical agents used in health care, like target microbes, level of activity, toxicity, and comments.

Germicidal Categories According to Chemical Group

Halogens, heavy metals, alcohols, phenolics compounds, oxidizers, aldehydes, detergents, and gases are chemical groups categorized by their germicidal properties.

Halogen Antimicrobial Chemicals

Fluorine, bromine, chlorine, and iodine are the halogen microbial chemicals.
Chlorine forms are microbicidal and sporicidal with longer exposure times.

Phenol and its Derivatives

Phenol coefficient compares a chemical's antimicrobial properties to those of phenol.
High concentrations are cellular poisons, and lower concentrations inactivate critical enzyme systems.

Chlorhexidine

A chlorinated complex organic base used to target cell membranes and protein structure.
Bactericidal for most bacteria types other than spores.
It has modest toxicity, is mild and acts quickly.

Alcohols as Antimicrobial Agents

Ethyl and isopropyl alcohols are common antimicrobial agents, working by dissolving lipids, disrupting surface tension, compromising membranes and through coagulation, dehydrating cells, and inhibiting growth.
More effective at inactivating enveloped viruses than nonenveloped viruses.

Germicidal effects are due to the direct and indirect actions of oxygen, forming hydroxyl free radicals.
These are highly toxic and reactive to microbes and are used when higher concentrations are needed.

Chemicals with Surface Action: Detergents

Surfactants, like detergents (anionic (-) and cationic (+)), have varying microbial action powers.
Cationic detergents are more effective by binding with bacterial surface proteins (due to the positive charge).
Soaps are weak microbicides, but their germicidal value increases when mixed with substances such as chlorhexidine or iodine.

Heavy Metal Compounds

Mercury, silver, gold, copper, arsenic, and zinc have been used.
Hg and Ag are significant germicides.
They act by binding to functional groups of proteins, inactivating them.
Drawbacks include toxicity to humans, allergic reactions, neutralization by biological fluids and wastes, and possible bacterial resistance development.

Aldehydes as Germicides

Aldehyde chemicals contain an -CHO functional group and include glutaraldehyde and formaldehyde (formalin).
Used for sterilization and high-level disinfection.

Gaseous Sterilants and Disinfectants

Ethylene oxide (ETO) and propylene oxide, and Chlorine dioxide are important gaseous sterilants and disinfectants.

Dyes as Antimicrobial Agents

Aniline dyes (crystal violet and malachite green) and Yellow acridine dyes (acriflavine and proflavine) are active against certain bacteria and fungi, but have limitations like staining and a narrow spectrum of activity.

Acids and Alkalis

Very low or high pH can damage or inhibit bacterial cells.
Limited by their corrosive, caustic, and hazardous nature.

Active Ingredients of Various Commercial Antimicrobial Products

Table listing various commercial antimicrobial products with their active chemical ingredients and antimicrobial categories.

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Description

Explore the essential methods for controlling microorganisms as detailed in Chapter 11 of 'Microbiology: A Systems Approach'. This quiz covers sterilization, disinfection, antisepsis, and the various physical and chemical agents used for microbial control. Test your understanding of microbial resistance and the effectiveness of different control techniques.