Tortora Chapter 7 - Tortora Chapter 7 Control of Microbial...

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Tortora Chapter 7 Control of Microbial Growth Consult Tables 7.1, 7.5, 7.8
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Terminology Sterilization-destruction of ALL forms of microbial life Commercial sterilization-apply just enough heat in food preparations to destroy endospores of Clostridium botulinum Disinfection-destruction of vegetative pathogens on inert surfaces Antisepsis-destruction of vegetative pathogens on living tissue
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Terms continued Degerming-mechanical removal of microbes in a limited area (alcohol swab before a shot) Sanitization-lowers microbial counts to ‘safe’ levels (washing then dipping in chemical disinfectant in a bar) icide-to kill stasis-to stop or to steady Aseptic-object or area is free of pathogens Asepsis-absence of significant contamination Sepsis-bacterial contamination
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Rate of microbial death Populations die at a specific rate when heated or treated with antimicrobial chemicals 1 million treated for 1 minute results in a death rate of 90% (leaves 100,000) Treat again, leaves 10,000 Treat again, leaves 1,000 Plot the curve logarithmically (see figure 7.1)
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Factors contributing to effectiveness of antimicrobial treatments 1. number of microbes (more takes longer) 2. environmental influences (organic matter like vomit or blood may harbor organisms) 3. Time of exposure (follow directions on bottles for maximum effectiveness) 4. microbial characteristics (some are just harder to kill due to virulence factors)
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Good web sites http://www.cellsalive.com/ecoli.htm
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Actions of microbial control agents 1. Alteration of membrane permeability-damage to lipids or proteins can cause leakage 2. Damage to proteins-heat can denature proteins by breaking hydrogen bonds, disulfide bridges 3. nucleic acids-DNA or RNA can be damaged by heat, radiation, or chemicals 4. Cell wall can be damaged (often the peptidoglycan layer is damaged)
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Physical methods of control Heat resistance varies among microorganisms TDP (thermal death point) is the lowest TEMPERATURE required to kill bacteria in a liquid suspension at a given time (10 minutes) TDT (thermal death time) is the lowest TIME required to kill bacteria in a liquid suspension at a set temperature DRT-decimal reduction time is the time in minutes in which 90% of population at a given temp. is killed
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Heat 1. Dry heat-(denature enzymes) oven (170 Degrees C for 2 hours and incineration (direct flame is an example) 2. moist heat-(coagulation of proteins) Boiling (20 minutes usually) Autoclave-steam under pressure (121 C-15 psi-15 minutes) Can’t use aluminum foil to steam!
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This note was uploaded on 03/26/2010 for the course BIO 3455 taught by Professor Bimbo during the Spring '10 term at 카이스트, 한국과학기술원.

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Tortora Chapter 7 - Tortora Chapter 7 Control of Microbial...

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