physical methods for killing microbes sterilization methods –incineration –autoclave –dry heat...
TRANSCRIPT
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PHYSICAL METHODS FOR KILLING MICROBES
• Sterilization methods– Incineration– Autoclave– Dry heat oven – Filter sterilization– Ultra violet light– Gamma radiation
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The direct flame represents a rapid sterilization method
Incineration
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The autoclave uses moist heat and pressure
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Boiling water involvesmoist heat
• This is not a reliable method for sterilization unless tyndallization is used.
• Why not?
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Pasteurization does not sterilize
• It is used to kill unwanted or harmful microbes
• Why doesn’t it sterilize?
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Hot-air (dry-heat) oven
Time and Temperature: 338F for 11/2 hours
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Filter Sterilization
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Filtration traps microorganisms
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Ultraviolet light can be used to control microbial growth
UV light attacks the cell’s DNA
What are some disadvantages in the use of UV for sterilization?
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The Ionizing and Electromagnetic Spectrum of Energies
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Thymine Dimers of DNA form when exposed to UV light
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Thymine Dimers
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CHECK MOLES FOR THESE CHANGES
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GAMMA RADIATION
A widely used method for sterilizing materials that would be adversely
altered by heat (plastics, lensed equip. heart-lung machines etc).
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Logo for gamma radiationLook for this logo on those foods that have been treated with gamma
radiation, such as meats, and produce.
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PRESERVATION METHODS
Drying (dehydration) Method
Salting Method
Low pH Method
Do these methods sterilize the food? Explain.
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General Principles ofChemical Control
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Resistance of microbes to chemical agents
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Disinfectants
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Killing Action of certain metals
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Killing Action of Some Antiseptics