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

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Microbiology (Biological Sciences)
Brian Lanoil

MICRB 265 October 25 2013 Microbial Growth ControlDeathfirstorder reaction o Dead vs Not deadEquation dCdtK o Cconcentration of cells o ttime elapsed o Kkill rateKill rate varies among organismsDecimal reduction times when only 10 of a population is left over are known for certain organisms o Important for determining sterilization times o Ex 100 organisms reduced to 1010 organisms reduced to 1 Logarithmic Destruction of CellsThe higher the temperature exposure the shorter the decimation time Factors that Affect Microbial ActivitiesPopulation sizePopulation composition o Different species are affected by different microbial agents in varying degreesConcentrationstrength of microbial agentDuration of exposure o The longer the exposure the more microbes killed offTemperatureo More killing at higher temperatures usuallyEnvironment o pH o salt concentration o viscosity Thermal KillingMoist heatdry heat o Disrupts hydrogen bondingBoiling water o Effective for vegetative cells and eukaryotic sporesAutoclave o Kills vegetative cells AND most bacterial endosporesComparison between dry heat killing vs autoclave in sterilizing glassware o Autoclave 15 minutes at 2atm o Dry heat in say an oven takes several hours zValueIs the increase in temperature needed to decimate reduce to 10 of original sizea microbial population aka reduce by 1 log PasteurizationOld Method vs Modern Method o Old method 15 minutes at 60degC o New method 15 seconds at 71degCIncreases shelf life but doesnt kill entire microbial population this is why milk spoils after some timeUsed for heatsensitive materials ex Beer milk wineGood against gve pathogens BUT NOT gve pathogens TyndalizationSequencial boiling o First boilingKills off vegetative cellsActivates spores tricks them into thinking that environmental conditions have change so they start becoming vegetative againabundance of nutrients encourages their growthOvernight incubation allows time for germination of spores o Second boilingKill off newly vegetative cellsResult No spores or vegetative cells presentsystem is nearly sterilized FiltrationFilters out most bacteria but NOT virusesHEPA highefficiency particulate air filter used in biological safety cabinets and clean rooms to remove microorganisms in the airOnly good for liquids and gases you cant filter a solid Ultraviolet and Ionizing RadiationUV o Surface sterilization o Cant penetrate through water glass or thick surfacesIonizing Radiation o Xrays gamma rays etc o Effectively penetrates ALL materialsResults in the formation of oxygen radicals that react with DNA of microorganismssterilization o Approved by FAD and WHO as a means to sterilize foodOxygen radicals are not present after object has been irradiated so consumption is not dangerous however you will get less nutrients as some of them have been damaged by the radiation Deinococcus radioduransIsolated from a nuclear reactorNot pathogenic thankfullyCan withstand 36Mrad o 10Krad wills humansPigment helps to protect it from radiation o Protects DNA repair mechanismsEach cell has multiple copies of chromosomes o If one is damages it can be patched up by using another Terminology of Chemical Control static prevents growth of organism in question cide kills organism in question Antimicrobial Agents Chemicals 1 Phenolics denature proteins via Hbond disruption a Used in hospitals and laboratories b DISINFECTANTS 2 Alcohols Same thing as Phenolics but alcohols also dissolve membrane lipids a Does not kill endospores
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