Microbiology Chapter 7: Desiccation & Radiation - Control of Microbial Growth Quiz

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Questions and Answers

What is the primary mechanism by which dry heat sterilization kills microorganisms?

Disruption of cell membranes

Oxidation (correct)

Denaturation of proteins

Dehydration

What is the main advantage of using filtration for sterilization?

It is a rapid method of sterilization

It is effective against all types of microorganisms

It is a low-cost method of sterilization

It can be used for thermolabile materials (correct)

What is the purpose of test strips in moist heat sterilization?

To detect the presence of microorganisms

To indicate sterility (correct)

To measure the temperature of the autoclave

To determine the pH of the solution

What is the minimum time required for sterilization of a 9000 ml fermentation bottle using moist heat?

70 minutes Signup and view all the answers

What type of organisms can survive pasteurization?

Thermoduric organisms Signup and view all the answers

What is the primary mechanism by which heat exerts its antimicrobial effect?

By denaturing enzymes and proteins Signup and view all the answers

What is the primary difference between high-temperature short-time (HTST) pasteurization and ultra-high-temperature (UHT) pasteurization?

The time required Signup and view all the answers

What is the term for the lowest temperature at which all cells in a liquid culture are killed in a certain time?

Thermal death point (TDP) Signup and view all the answers

What is the purpose of the perforated shelf in an autoclave?

To allow for the circulation of steam Signup and view all the answers

What is the minimum temperature and time required for moist heat sterilization in an autoclave?

121°C for 15 min Signup and view all the answers

What is the function of the operating valve in an autoclave?

To control the steam flow Signup and view all the answers

What is the decimal reduction time (DRT) equivalent to?

The time required to reduce the viable bacteria by 90% Signup and view all the answers

What is the function of the steam jacket in an autoclave?

To distribute the steam evenly Signup and view all the answers

What is the purpose of the exhaust valve in an autoclave?

To release the steam after sterilization Signup and view all the answers

What is the main difference between sterilization and disinfection?

Sterilization focuses on removing microbial life, while disinfection targets only harmful microorganisms Signup and view all the answers

What is the term for the mechanical removal of microbes from a limited area?

Degerming Signup and view all the answers

What is the term for the absence of significant contamination?

Asepsis Signup and view all the answers

What is the mechanism of action that affects the metabolic pathways of microorganisms?

Damage to proteins Signup and view all the answers

What is the term for the process of lowering microbial counts on eating utensils to safe levels?

Sanitization Signup and view all the answers

What is the term for treatments that kill microorganisms?

Biocide Signup and view all the answers

What is the primary mechanism by which high pressure controls microbial growth?

Denaturation of proteins Signup and view all the answers

Which of the following types of radiation does not cause damage to DNA?

Infrared radiation Signup and view all the answers

What is the purpose of the cotton plug in the vacuum line in the sterile filtration setup?

To ensure sterility of the vacuum line Signup and view all the answers

Which of the following physical methods of microbial control uses salts and sugars to create a hypertonic environment?

Osmotic pressure Signup and view all the answers

What is the optimal pH range for the effective use of chlorine as a disinfectant?

pH 5.5-7.5 Signup and view all the answers

What is the primary mechanism by which refrigeration controls microbial growth?

Bacteriostatic effect Signup and view all the answers

What is the purpose of the membrane filter in the sterile filtration setup?

To filter out microbial contaminants Signup and view all the answers

What is the primary mechanism by which lyophilization (freeze-drying) controls microbial growth?

Absence of water prevents metabolism Signup and view all the answers

Study Notes

The Terminology of Microbial Control

Sepsis refers to bacterial contamination
Asepsis is the absence of significant contamination
Sterilization removes and destroys all microbial life
Commercial sterilization kills C.botulinum endospores from canned goods
Disinfection destroys harmful microorganisms
Antisepsis destroys harmful microorganisms from living tissue
Degerming is the mechanical removal of microbes from a limited area
Sanitization lowers microbial counts on eating utensils to safe levels
Biocide (germicide) treatments kill microbes
Bacteriostasis inhibits, but does not kill, microbes

Actions for Microbial Control

There are three main mechanisms of action:
- Alteration of membrane permeability (Targeting the cell wall structure)
- Damage to proteins (Affecting the metabolic pathways)
- Damage to nucleic acids

Physical Methods of Microbial Control

Heat denatures enzymes
Thermal death point (TDP) is the lowest temperature at which all cells in a liquid culture are killed in a certain time (e.g., 10 min)
Thermal death time (TDT) is the minimal time for all bacteria in a liquid culture to be killed at a particular temperature
Decimal reduction time (DRT) is the number of minutes of exposure to a defined temperature to reduce viable bacteria by 90%

Moist Heat Sterilization

Moist heat denatures proteins
Boiling, free-flowing steam, and autoclaving (steam under pressure at 121°C for 15 min) kill all organisms and endospores
Steam must contact the item's surface
Large containers require longer sterilization times
Test strips are used to indicate sterility
Not all objects can withstand moist heat sterilization
Example sterilization times: test tube (15 min), Erlenmeyer flask (2000ml) (30 min), fermentation bottle (9000 ml) (70 min)

Heat

Pasteurization reduces spoilage organisms and pathogens using HTST (72°C for 15 sec) or UHT (140°C for 4 sec)
Thermoduric organisms survive pasteurization

Dry Heat Sterilization

Kills by oxidation using flaming, incineration, or hot-air sterilization

Filtration

Passage of substance through a screen-like material
Used for heat-sensitive materials
High-efficiency particulate air (HEPA) filters remove microbes >0.3 µm
Membrane filters remove microbes >0.22 µm

Other Physical Methods

Low temperature has a bacteriostatic effect using refrigeration, deep-freezing, or lyophilization
High pressure denatures proteins
Desiccation prevents metabolism due to the absence of water
Osmotic pressure uses salts and sugars to create a hypertonic environment, causing plasmolysis

Radiation

Ionizing radiation (X-rays, gamma rays, electron beams) ionizes water, creating reactive hydroxyl radicals that damage DNA, causing lethal mutations
Nonionizing radiation (UV, 260 nm) damages DNA by creating thymine dimers
Microwaves kill by heat, not especially antimicrobial

Chemical Methods

Concentration of disinfectant is important: different disinfectants work better at different concentrations
Organic matter interferes with disinfection
pH affects disinfection: chlorine is most effective between pH 5.5-7.5
Time is a factor in disinfection

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Description

This quiz covers the terminology and concepts related to the control of microbial growth, including sepsis, asepsis, and aseptic surgery techniques.

Microbiology Chapter 7: The Control of Microbial Growth

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