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Lecture

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

67 Pages
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Department
Microbiology (Biological Sciences)
Course Code
MICRB265
Professor
Brian Lanoil

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MICRB 265 (October 25, 2013)
Microbial Growth Control
Death = first-order reaction
o Dead vs. Not dead
Equation: dC/dt = K
o C = concentration of cells
o t = time elapsed
o K = kill rate
Kill rate varies among organisms
Decimal 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 10
10 organisms reduced to 1
Logarithmic Destruction of Cells
The higher the temperature exposure, the shorter the decimation time
Factors that Affect Microbial Activities
Population size
Population composition
o Different species are affected by different microbial agents in varying degrees
Concentration/strength of microbial agent
Duration of exposure
o The longer the exposure, the more microbes killed off
Temperature
o More killing at higher temperatures (usually)
Environment
o pH
o salt concentration
o viscosity
Thermal Killing
Moist heat > dry heat
o Disrupts hydrogen bonding
Boiling water
o Effective for vegetative cells and eukaryotic spores
Autoclave
o Kills vegetative cells AND most bacterial endospores
Comparison 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
z-Value
Is the increase in temperature needed to decimate (reduce to 10% of original size ) a
microbial population (aka reduce by 1 log)
Pasteurization
Old Method vs. Modern Method
o Old method: 15 minutes at 60deg.C
o New method: 15 seconds at 71deg.C
Increases shelf life (but doesn’t kill entire microbial population… this is why milk spoils
after some time)
Used for heat-sensitive materials (ex. Beer, milk, wine)
Good against g-ve pathogens BUT NOT g+ve pathogens
Tyndalization
Sequencial boiling
o First boiling
Kills off vegetative cells
Activates spores (tricks them into thinking that environmental conditions
have change so they start becoming vegetative again) abundance of
nutrients encourages their growth
Overnight incubation (allows time for germination of spores)
o Second boiling
Kill off newly vegetative cells
Result: No spores or vegetative cells present system is nearly sterilized
Filtration
Filters out most bacteria but NOT viruses
HEPA (high-efficiency particulate air) filter used in biological safety cabinets and clean
rooms to remove microorganisms in the air
Only good for liquids and gases (you can’t filter a solid!)
Ultraviolet and Ionizing Radiation
UV
o Surface sterilization
o Cant penetrate through water, glass, or thick surfaces
Ionizing Radiation
o X-rays, gamma rays, etc
o Effectively penetrates ALL materials
Results in the formation of oxygen radicals that react with DNA of
microorganisms… sterilization
o Approved by FAD and WHO as a means to sterilize food
Oxygen 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 radiodurans
Isolated from a nuclear reactor
Not pathogenic (thankfully!)
Can withstand 3-6Mrad
o 10Krad wills humans
Pigment helps to protect it from radiation
o Protects DNA repair mechanisms
Each 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 H-bond 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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Description
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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