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Questions and Answers
The ____________ death point is the lowest temperature at which all the microbes in a liquid culture will be killed in 10 minutes.
The ____________ death point is the lowest temperature at which all the microbes in a liquid culture will be killed in 10 minutes.
thermal
Moist heat kills microbes by ____________ enzymes.
Moist heat kills microbes by ____________ enzymes.
denaturing
Autoclaving is the most effective method of moist heat ____________.
Autoclaving is the most effective method of moist heat ____________.
sterilization
Dry heat kills by ____________.
Dry heat kills by ____________.
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Filtration is the passage of a liquid or gas through a filter with pores small enough to retain ____________.
Filtration is the passage of a liquid or gas through a filter with pores small enough to retain ____________.
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Methods that produce the same effect are called equivalent ____________.
Methods that produce the same effect are called equivalent ____________.
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Chemical agents are used on living tissue as ______ and on inanimate objects as disinfectants.
Chemical agents are used on living tissue as ______ and on inanimate objects as disinfectants.
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Careful attention should be paid to the ______ and concentration of the disinfectant to be used.
Careful attention should be paid to the ______ and concentration of the disinfectant to be used.
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The ______ test is used to determine bacterial survival in the manufacturer’s recommended dilution of a disinfectant.
The ______ test is used to determine bacterial survival in the manufacturer’s recommended dilution of a disinfectant.
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The ______ method is used to evaluate the effectiveness of agents against viruses, endospore-forming bacteria, mycobacteria, and fungi.
The ______ method is used to evaluate the effectiveness of agents against viruses, endospore-forming bacteria, mycobacteria, and fungi.
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Phenolics exert their action by ______ plasma membranes.
Phenolics exert their action by ______ plasma membranes.
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The germicidal action of chlorine is based on the formation of ______ acid when chlorine is added to water.
The germicidal action of chlorine is based on the formation of ______ acid when chlorine is added to water.
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Microbes can be removed from air by high-efficiency particulate air (______) filters.
Microbes can be removed from air by high-efficiency particulate air (______) filters.
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Membrane filters composed of ________ esters are commonly used to filter out bacteria, viruses, and even large proteins.
Membrane filters composed of ________ esters are commonly used to filter out bacteria, viruses, and even large proteins.
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The effectiveness of low ________ depends on the particular microorganism and the intensity of the application.
The effectiveness of low ________ depends on the particular microorganism and the intensity of the application.
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High ________ denatures proteins in vegetative cells.
High ________ denatures proteins in vegetative cells.
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Microorganisms in high concentrations of salts and sugars undergo ________.
Microorganisms in high concentrations of salts and sugars undergo ________.
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The most effective germicidal wavelength of ultraviolet (UV) radiation is ________ nm.
The most effective germicidal wavelength of ultraviolet (UV) radiation is ________ nm.
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Silver, mercury, copper, and zinc exert their antimicrobial action through ______ action.
Silver, mercury, copper, and zinc exert their antimicrobial action through ______ action.
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When heavy metal ions combine with ______ groups, proteins are denatured.
When heavy metal ions combine with ______ groups, proteins are denatured.
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[Blank] are cationic detergents attached to NH4+ that disrupt plasma membranes.
[Blank] are cationic detergents attached to NH4+ that disrupt plasma membranes.
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Nitrate and nitrite salts prevent germination of C.botulinum ______ in meats.
Nitrate and nitrite salts prevent germination of C.botulinum ______ in meats.
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Aldehydes such as formaldehyde and glutaraldehyde are among the most effective chemical ______.
Aldehydes such as formaldehyde and glutaraldehyde are among the most effective chemical ______.
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Hydrogen peroxide, peracetic acid, benzoyl peroxide, and ozone exert their antimicrobial effect by ______ molecules inside cells.
Hydrogen peroxide, peracetic acid, benzoyl peroxide, and ozone exert their antimicrobial effect by ______ molecules inside cells.
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Study Notes
Physical Methods of Microbial Control
- Heat is a primary method to kill microorganisms and can be applied in various forms.
- Thermal Death Point (TDP): Lowest temperature to kill all microbes in liquid culture within 10 minutes.
- Thermal Death Time (TDT): Time required to kill all bacteria in a liquid culture at a specified temperature.
- Decimal Reduction Time (DRT): Time needed to kill 90% of a bacterial population at a specific temperature.
- Moist heat denatures enzymes to kill microbes efficiently.
- Boiling (100°C) eliminates many vegetative cells and viruses in approximately 10 minutes.
- Autoclaving: Most effective moist heat sterilization method utilizing steam under pressure.
- HTST Pasteurization: Uses high temperature (72°C for 15 seconds) to eliminate pathogens without impacting food flavor.
- UHT Treatment: Employs 140°C for 4 seconds to sterilize dairy products.
- Dry heat sterilization methods include direct flaming, incineration, and hot-air sterilization, functioning through oxidation.
- Equivalent treatments produce similar effects in reducing microbial growth, allowing for alternative methods.
Filtration
- Filtration involves passing liquids or gases through filters that retain microbes.
Chemical Methods of Microbial Control
- Chemical agents serve dual purposes: as antiseptics on living tissues and disinfectants on inanimate objects; few achieve sterility.
- Effective disinfection depends on disinfectant properties, concentration, presence of organic matter, contact degree, and temperature.
- Use-Dilution Test: Evaluates bacterial survival in recommended disinfectant dilutions and is applicable for various microorganisms.
- Disk-Diffusion Method: Tests efficacy of chemical agents using soaked filter paper on inoculated agar plates to observe inhibition zones.
Types of Disinfectants
- Phenolics: Damage plasma membranes; hexachlorophene is a common skin disinfectant.
- Biguanides: Compromise plasma membranes of vegetative cells.
- Iodine: Inactivates enzymes and proteins via interaction with amino acids.
- Chlorine: Forms hypochlorous acid in water producing germicidal effects.
- Alcohols: Denature proteins and dissolve lipids; tinctures enhance antimicrobial effectiveness.
- HEPA Filters: Efficiently remove microbes from air; cellulose ester membrane filters target bacteria and viruses.
Low Temperatures
- Low temperatures inhibit microbial growth; most do not reproduce at refrigerator levels (0–7°C).
- Many microbes can survive but do not proliferate at subzero temperatures for food storage.
High Pressure
- High pressure leads to denaturation of proteins in vegetative cells.
Desiccation
- Microorganisms cannot grow without water, although some can remain viable.
- Viruses and endospores show resistance to desiccation.
Osmotic Pressure
- High concentrations of salts and sugars cause plasmolysis in microorganisms.
- Molds and yeasts demonstrate superior growth capabilities under low moisture or high osmotic pressure.
Radiation
- The impact of radiation varies with wavelength, intensity, and exposure duration.
- Ionizing Radiation: Includes gamma rays, X-rays, and high-energy electrons, largely affecting water in cells to form reactive hydroxyl radicals.
- UV Radiation: Non-ionizing, with low penetration ability; most effective at 260 nm causing thymine dimers that interfere with DNA replication.
- Microwaves kill microbes indirectly by heating materials.
Chemical Disinfectants Mechanisms
- Heavy metals (silver, mercury, copper, zinc) act via oligodynamic action, denaturing proteins by binding to sulfhydryl groups.
- Soaps have limited germicidal effects but are effective in removing microorganisms.
- Acid-Anionic Detergents: Used for cleaning dairy equipment.
- Quats: Cationic detergents disrupting plasma membranes.
- Food Preservatives: Substances like SO2, sorbic acid, and nisin inhibit microbial growth in food products.
Sterilization Agents
- Aldehydes: Formaldehyde and glutaraldehyde are potent disinfectants through protein inactivation.
- Ethylene Oxide: Common gas for sterilization, penetrates materials and denatures proteins.
- Plasma Gases: Utilize free radicals for sterilization purposes.
- Supercritical Fluids: Sterilize at low temperatures, combining liquid and gas properties.
- Hydrogen Peroxide and Ozone: Oxidize cellular molecules to exhibit antimicrobial effects.
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Description
This quiz covers the physical methods of microbial control, including the use of heat to kill microorganisms. It also discusses thermal death point, thermal death time, and decimal reduction time.
