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Sypes
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Time required to kill all the target microbes at a specific temperature
Thermal Death Time
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The temperature at which an organism is killed in 10 minutes
Thermal Death Point
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Direct flame; loop in Bunsen burner; disposable materials
Incineration
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Care should be taken to be sure pathogens do not escape the flame before they are killed
Incineration
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Hot air oven at 160 C for 1.5 to 2 hours
Dry heat
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Powders, glassware; used on materials that cannot withstand moisture
Dry heat
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Penetrates more rapidly than dry heat
Moist heat
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100 C for 10 minutes will kill vegetative forms
Boiling water
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Viruses & spores: 2 hours; not a very reliable method
Boiling water
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Most dependable method; steam under pressure; 121 C at 15 psi for 15 mins
Autoclave
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Limitations: plastic ware melts, sharp instruments become dull, some chemicals break down; Bacillus stearothermophilus used as a control
Autoclave
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Fractional sterilization; steam at 100 C for 3 minutes on 3 successive days
Tyndallization
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Used for liquids and heat- sensitive materials
Tyndallization
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Not a method of sterilization; destroys pathogens and organisms that cause spoilage and reduces bacterial count
Pasteurization
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Pasteurization is aimed at destroying
- Mycobacterium tuberculosis- TB
- Brucella abortus- undulant fever
- Coxiella burnetii- Q fever
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Device for removing microbes from a solution
Filtration
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Pad of porcelain or ground glass
Inorganic filters
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Use diatomaceous earth (remains of marine algae); swimming pool, aquarium filters
Organic filters
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Pad of cellulose
Membrane filters
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Valuable because colonies will form on pad and can be counted
Acetate
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265 nm is most destructive to bacteria (visible light: 400- 800 nm)
Ultraviolet light
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Cannot penetrate solids or liquids; reduces airborne or surface contamination
Ultraviolet light
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Ionizing (high energy) radiation used to sterilize vitamins, hormones, and antibiotics; break chemical bonds
X- rays or gamma rays
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No specific activity against microbes other than heat generation
Microwaves
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Sound waves with frequencies beyond the range of human hearing are passed through a fluid; used for fluids
Ultrasound
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High frequency sound waves cause formation of bubbles or cavities. The cavities collapse and send out shock waves which destroy microbes
Cavitation
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Few practical applications; geneticists split cells to study organelles, dentists use sonicare
Cavitation
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