6-Control_of_Microorganisms_Feb7

6-Control_of_Microorganisms_Feb7 - Control of...

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Control of microorganisms Chap 26
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An4microbial Control Steriliza)on: The killing or removal of all viable organisms (including endospores). Inhibi)on: Effec4vely limi4ng microbial growth. Decontamina)on: The treatment of an object to make it safe to handle. Disinfec)on : Directly targets the removal of all pathogens , not necessarily all microorganisms Physical methods: Heat Radia4on Filtra4on Chemical methods (called an4microbials): Used on external surfaces: Sterilants, disinfectants, sani4zers, an4sep4cs. Used internally: an4bio4cs, an4virals, an4fungals.
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1. Physical methods: heat Heat is the most widely used method for controlling microbial growth High temperatures denature macromolecules Amount of time required to reduce viability tenfold is called the decimal reduction time (D). The decimal reduction time is inversely correlated with the temperature. The time necessary to kill a defined fraction is independent of the initial cell concentration (90%). Different microorganisms have different decimal reduction times: A, mesophile; B, thermophile. Decimal reduction time (D) Time (min) Survival fraction (log scale) 70C 60C 50C Temperature (C) Decimal reduction time (min) A B Brock Biology of Microorganisms, 13 th Edition.
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Example A) D = 1h, CFU T0 = 10 7 B) D = 3.3 h, CFU T0 = 10 7 For A, how much 4me is needed to have <1 CFU? How much 4me for B?
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Heat Steriliza4on The thermal death time is the time needed to kill all cells at a given temperature. It is dependent on the population size of the microorganism tested. Need to standardize the starting number of cells to be able to compare the sensitivity of different microorganisms. Endospores survive heat that would rapidly kill vegetative cells. A higher temperature is needed to kill endospores. Endospores can resist boiling for a long time: 5 min for a decimal reduction. The autoclave is a sealed device that uses steam under pressure: Allows temperature of water to get above 100 ° C. At 15 psi (pound/square inch), steam reaches 121 ° C, sterilization is achieved in 10-15 min. The object being sterilized will reach this temperature. Not suitable for heat- sensitive object/liquid. It is not the pressure that kills microorganisms, but the high temperature.
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Chamber pressure gauge Steam exhaust valve Door Thermometer and valve Steam supply valve Steam enters here Steam exhaust Jacket chamber Air exits through vent Total cycle time (min) Temperature (C) Autoclave time Stop steam Begin pressure Flowing steam Sterilization time Temperature of object being sterilized Temperature of autoclave Brock Biology of Microorganisms, 13 th Edition.
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1. Physical methods: pasteuriza4on Pasteurization is the process of using precisely controlled heat to reduce the microbial load in heat-sensitive liquids Does not kill all organisms, it is not a method of sterilization.
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