MICRB265 Lecture : MICRB 265 Lecture Note BUNDLE (October 23 - December 4)

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Death = first-order reaction: dead vs. not dead. Equation: dc/dt = k: c = concentration of cells, t = time elapsed, k = kill rate. Decimal reduction times (when only 10% of a population is left over) are known for certain organisms. The higher the temperature exposure, the shorter the decimation time. Population composition: different species are affected by different microbial agents in varying degrees. Duration of exposure: the longer the exposure, the more microbes killed off. Temperature: more killing at higher temperatures (usually) Moist heat > dry heat: disrupts hydrogen bonding. Boiling water: effective for vegetative cells and eukaryotic spores. Autoclave: kills vegetative cells and most bacterial endospores. Comparison between dry heat killing vs. autoclave in sterilizing glassware: autoclave: 15 minutes at 2atm, dry heat (in, say, an oven) takes several hours z-value. Is the increase in temperature needed to decimate (reduce to 10% of original size ) a microbial population (aka reduce by 1 log)

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