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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 ____________.
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 ____________.
Methods that produce the same effect are called equivalent ____________.
Methods that produce the same effect are called equivalent ____________.
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.
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.
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.
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.
Phenolics exert their action by ______ plasma membranes.
Phenolics exert their action by ______ plasma membranes.
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.
Microbes can be removed from air by high-efficiency particulate air (______) filters.
Microbes can be removed from air by high-efficiency particulate air (______) filters.
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.
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.
High ________ denatures proteins in vegetative cells.
High ________ denatures proteins in vegetative cells.
Microorganisms in high concentrations of salts and sugars undergo ________.
Microorganisms in high concentrations of salts and sugars undergo ________.
The most effective germicidal wavelength of ultraviolet (UV) radiation is ________ nm.
The most effective germicidal wavelength of ultraviolet (UV) radiation is ________ nm.
Silver, mercury, copper, and zinc exert their antimicrobial action through ______ action.
Silver, mercury, copper, and zinc exert their antimicrobial action through ______ action.
When heavy metal ions combine with ______ groups, proteins are denatured.
When heavy metal ions combine with ______ groups, proteins are denatured.
[Blank] are cationic detergents attached to NH4+ that disrupt plasma membranes.
[Blank] are cationic detergents attached to NH4+ that disrupt plasma membranes.
Nitrate and nitrite salts prevent germination of C.botulinum ______ in meats.
Nitrate and nitrite salts prevent germination of C.botulinum ______ in meats.
Aldehydes such as formaldehyde and glutaraldehyde are among the most effective chemical ______.
Aldehydes such as formaldehyde and glutaraldehyde are among the most effective chemical ______.
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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