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9 Cards in this Set
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Factors influencing success of control methods
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Control of microbial growth can aprevent infections and food spoilage.
Sterilaztion (destroying all microbial life on an object) Heat of canned food to destroy C. botulisum endospores. disinfection -forf nonliving surface antisepsis to reduce or inhibitg microorganisms on living tissue. suffix cide means to kill suffix stat means to inhibit sepsis is bacterial contamination |
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factors influencing success of control methods
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Number and Nature of microorganisms
The time it takes to kill a microbial pop. is proportional to the # of microbes. Microbial species and life cycle phases eg. endospores have diff. susceptibilities to physical and chemical controls. Organic matter may interfere with heat trts and chemical control agents. Longer exposure to lower heat can produce the same effect as shorter time at higher heat. |
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strength of control agent
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some microbial control agents damage cellular proteins by breaking hydrogen and covalent bonds.
other agents interfere with DNA and RNA replication and protein synthesis. |
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Time, temperature, and ph
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heat, moist heat by denaturing enzymes.
Thermal death point TDP is lowest temp at which all the bacteria in a liquid cult. will be killed in 10 mins. DRT Decimal reduction time is the length of time in which 90% of a bacterial population will be killed at a given temp. boiling 100 C kills many vegatative cells and viruse with in 10 mins. Autoclaving pasteruization Dry heat sterilization Different methods that produce the same effect (reductiond in microbial growth) are called equivalent treatments. Filtration By air by high effeciencyh particulate air filters. Membrane filters composed of nitrocellulose or cellulose acetate to filter out bacteria, viruses and large proteins. |
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cont
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Desiccation- abscence of water, microorganisms cannot grow
Viruses and endospores can resist desiccaton Osmotic pressure- Microorganisms in high concentrations of salts and sugars undergo plasmolysis. Molds and yeasts are more capable than bacteria of growing in materials with low moisture or high osmotic pressure. radiation |
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Conditions influencing microbial growth
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chemical disinfectants is affected by the type of microorganism and the physical environment.
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chemical methods of control
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chemical agents are used on living tissue (antispectics and on inanimate objects disinfectants)
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chemical agents
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halogens- Iodine & chlorine
alcohols-denature proteins and dissolve lipids phenols-injure plasma membranes, inactivate enzymes and denature proteins heavy metals-silver, mercury, copper and zinc are used as germicidals. aldehydes-inactivate proteins gases- ozone, peroxide and peracetic acid are used. oxidize molecules inside cells. detergents- peroxides dyes gram neg more resistant than gram pos. to disinfectants and antiseptics. endospores and mycobacteria are very resistant to disinfects and antiseptics. nonenveloped viruses are gen. more resistant than enveloped viruses to disinfectants and antiseptics. |
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Tests for effectiveness of antiseptics and disinfectants
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a. phenol coefficient test-phenolics exert their action by injuring plasma membranes, inactivating enzymes, and denaturing proteins.
common phenolics are cresols and hexachlorophene. |
