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Questions and Answers
What term describes agents that kill microorganisms?
What term describes agents that kill microorganisms?
What is the primary purpose of pasteurization?
What is the primary purpose of pasteurization?
Which of the following methods is the most effective moist heat method for sterilization?
Which of the following methods is the most effective moist heat method for sterilization?
What temperature is recommended for normal pasteurization?
What temperature is recommended for normal pasteurization?
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Which method involves the direct application of heat to destroy microorganisms?
Which method involves the direct application of heat to destroy microorganisms?
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How does slow freezing affect microorganisms?
How does slow freezing affect microorganisms?
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What range of temperatures may inhibit the reproduction of certain organisms through freezing?
What range of temperatures may inhibit the reproduction of certain organisms through freezing?
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What is the optimum concentration of alcohols like ethanol and isopropanol for effective antiseptic action?
What is the optimum concentration of alcohols like ethanol and isopropanol for effective antiseptic action?
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What defines -static agents in microbial control?
What defines -static agents in microbial control?
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Which of the following best describes the action of heavy metals like mercury and silver in antiseptic practice?
Which of the following best describes the action of heavy metals like mercury and silver in antiseptic practice?
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What is a characteristic of quaternary ammonium compounds in terms of their antimicrobial action?
What is a characteristic of quaternary ammonium compounds in terms of their antimicrobial action?
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Which of the following substances is an example of a halogen used in antiseptic practices?
Which of the following substances is an example of a halogen used in antiseptic practices?
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How do antibiotics primarily function against bacterial infections?
How do antibiotics primarily function against bacterial infections?
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Which of the following is NOT a mode of action for disinfectants mentioned in the content?
Which of the following is NOT a mode of action for disinfectants mentioned in the content?
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What role does soap play in antiseptic action?
What role does soap play in antiseptic action?
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Which of the following substances is used as an algicide?
Which of the following substances is used as an algicide?
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What is the primary mechanism by which ionizing radiation preserves food?
What is the primary mechanism by which ionizing radiation preserves food?
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Which type of radiation is primarily used in food preservation but has low penetration?
Which type of radiation is primarily used in food preservation but has low penetration?
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What is the main action of bleach as a disinfectant?
What is the main action of bleach as a disinfectant?
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Which of the following statements about quaternary ammonium compounds is true?
Which of the following statements about quaternary ammonium compounds is true?
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Which microorganisms are relatively resistant to ionizing radiation?
Which microorganisms are relatively resistant to ionizing radiation?
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What is the effect of microwave radiation on microorganisms?
What is the effect of microwave radiation on microorganisms?
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What role do preservatives play in products?
What role do preservatives play in products?
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What is a common use of disinfectants like bleach?
What is a common use of disinfectants like bleach?
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What effect does extreme heat have on proteins?
What effect does extreme heat have on proteins?
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How does damage to a viral envelope affect viral replication?
How does damage to a viral envelope affect viral replication?
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What is the role of HEPA filters in microbiology?
What is the role of HEPA filters in microbiology?
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What does minimum inhibitory concentration (MIC) measure?
What does minimum inhibitory concentration (MIC) measure?
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What can cause plasmolysis in microbial cells?
What can cause plasmolysis in microbial cells?
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What is a common effect of damaging nucleic acids?
What is a common effect of damaging nucleic acids?
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What happens to cellular contents when the cytoplasmic membrane is damaged?
What happens to cellular contents when the cytoplasmic membrane is damaged?
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What do non-enveloped viruses exhibit compared to enveloped viruses?
What do non-enveloped viruses exhibit compared to enveloped viruses?
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What does a zone of inhibition indicate when using the disc diffusion method?
What does a zone of inhibition indicate when using the disc diffusion method?
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Which of the following is NOT a common foodborne pathogen?
Which of the following is NOT a common foodborne pathogen?
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What is the function of ELISA in immunological methods?
What is the function of ELISA in immunological methods?
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Which method is used to analyze genomic markers for microbial identification?
Which method is used to analyze genomic markers for microbial identification?
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Which one of the following is a limitation of conventional culturing methods?
Which one of the following is a limitation of conventional culturing methods?
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What technology does FISH utilize in molecular methods?
What technology does FISH utilize in molecular methods?
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Which of the following factors influences the choice of microbial identification method?
Which of the following factors influences the choice of microbial identification method?
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Which molecular method involves amplification of DNA?
Which molecular method involves amplification of DNA?
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Study Notes
Microbial Control and Detection
- Microbial control involves inhibiting or preventing microorganism growth.
- This is achieved by either killing microorganisms or inhibiting their growth.
- Cidal agents kill cells; static agents inhibit growth without killing.
- Pathogens can cause illness, disease, or death, impacting food safety.
- Spoilage microorganisms affect food quality, leading to poor quality, off-flavors, and short shelf-life.
Methods of Microbial Control
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Physical Methods:
- Heat Radiation: Boiling, pasteurization, and autoclaving are inexpensive and effective methods. Pasteurization reduces pathogens without altering flavor; different techniques involve varying temperatures and times (ultra-pasteurization, flash pasteurization, normal pasteurization). Autoclaving (steam under pressure) is the most effective moist heat method (typically 121.5°C at 15 psi for 15 minutes).
- Dry Heat: Incineration or hot air (160-170°C) can kill microorganisms. Dry heat methods can be useful for materials sensitive to high heat or moisture.
- Freezing: Temperatures between 0° and 7°C typically inhibit microorganism reproduction, but quick freezing is often used for long-term storage whereas slow freezing can be bactericidal.
- Desiccation: Drying or freeze-drying inhibits growth (via enzyme inhibition) though microorganisms remain viable.
- Radiation: Ionizing radiation (e.g., alpha, beta, gamma, x-rays) penetrates materials, denaturing proteins and nucleic acids, affecting microbial growth/killing in food. Ultraviolet (UV) radiation, which is non-ionizing, has a low degree of penetration, causing thymine dimers in DNA that interferes with DNA replication.
- Filtration: Removes microorganisms. HEAP filters remove particles at least 99.97% of 0.3 micrometers in diameter; ULPA filters are even more effective at removing smaller particles (120 nanometers or larger).
- Osmotic Pressure: Extremely hypertonic conditions cause cell shrinkage/plasmolysis due to water loss.
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Chemical Methods:
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Disinfectants: Antimicrobial agents used on inanimate objects.
- Bleach (sodium hypochlorite) is effective against microorganisms and HIV and acts by inhibiting enzyme activity and oxidizing cells causing harm to bacteria. Concentrations must be high enough to be effective considering the amount of organic materials potentially present.
- Other Disinfectants(non-bleach): utilize quaternary ammonium compounds (often found in Lysol); they denature proteins and disrupt cell membrane permeability which cause cellular content leaks.
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Antiseptics: Antimicrobial agents used on living tissues.
- Alcohols (ethanol, isopropyl alcohol): Denature proteins and dissolve lipids; an optimum concentration of 70% is often effective.
- Soap and surface-active ingredients:
- Acid-anionic detergents: sanitize;
- Quaternary ammonium compounds (Quats): sanitize and are bactericidal, denaturing proteins and disrupting cell membranes.
- Heavy metals: oligodynamic action, toxic effects; examples like Mercury, Copper, Silver, and Zinc are used against some microbes, and can harm cells by denaturing proteins.
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Disinfectants: Antimicrobial agents used on inanimate objects.
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Biological Methods: Antiobiotics which destroy or slow the growth of bacteria causing illness. They are used to treat bacterial infections though they are ineffective against viruses.
Testing and Measuring Antimicrobial Activity
- Protocol for testing control agents: The general protocol includes exposing the microorganism to the agent, removing the agent, placing the organism in a medium for growth, and observing for reproduction.
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Measuring antimicrobial activity:
- Minimum inhibitory concentration (MIC): The smallest amount of an antimicrobial agent needed to prevent test organism growth.
- Using dilution methods, different concentrations of the agent are prepared and inoculated in different tubes/plates.
- Disc diffusion method: A disk soaked with a chemical is placed on an inoculated agar plate; a zone of inhibition indicates efficacy.
Relative Susceptibility of Microorganisms
- Relative susceptibility and resistance to controls vary across organisms (e.g. enveloped viruses are most susceptible, bacterial endospores are most resistant).
Detecting Microbial Contamination in Food/Fish
- Lab methods for identifying microbial hazards in food/fish include conventional culturing, immunological, and molecular methods.
- Spectroscopic methods such as MALDI-TOF and Raman spectroscopy are emerging. The choice of method depends on technology, risks, sample complexity, speed, and microbial load.
Common Foodborne Pathogens
- Examples of foodborne pathogens include Salmonella, Campylobacter, Listeria monocytogenes, and E. coli O157:H7.
Conventional Culturing Methods
- These methods involve serial dilutions and plating to isolate and identify microorganisms. They often involve preparing, pre-enrichment, plating, colony selection, biochemical testing (which depends on organism being studied ) and confirmation steps.
Immunological Methods
- These methods identify microbial contamination/pathogens via antibody-based tests, like ELISA and microarrays. Serological tests and microarrays are often used, involving identifying antibodies specific to known pathogens.
Molecular Methods
- These use DNA and RNA to identify/analyse microorganisms. Methods include FISH (fluorescent in situ hybridization), amplification methods (e.g., PCR, qPCR, rt-PCR), DNA microarrays, and whole-genome sequencing.
Spectroscopic Methods
- These methods identify organisms on grounds of protein profiles (like MALDI-TOF) or chemical compounds/inclusions (like Raman). Rapid detection and identification are usually possible with these technologies.
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