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Microbiology Chatper 24 Microbial Control.txt
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Sterilization
No life
Sanitization
Reduce number of microbes to a safe level
Physical Methods of Control
Heat
Heat Is One of the Most Common Physical Control Methods
Sterilizes
At heats above the growth range:
proteins and nucleic acids are destroyed
water is removed
Each microbial species has a thermal death time
for a given temperature
Each species has a thermal death point:
the minimum temperature at which it dies in a given time period
Incineration uses
direct flame to kill microbes
Dry heat requires
Long periods of exposure to high temperatures
The heat changes microbial proteins and removes water, slowly burning the microbes
Moist heat (like boiling water) is
Faster and more effective at a lower temperature than dry heat
It kills microbes by denaturing their proteins
Boiling water may NOT
Kill all spores or inactivate all viruses
Boiling water
Denatures proteins
10 min for most bacteria
30 min for some fungal and protozoan spores
2 hours for bacterial spores
30 min is the minimum for safety
Autoclave
Sterilization chamber
When you increase pressure you can increase temperature
Normal is 15 lbs/sq in = 121.5C
Rusts sharp instruments
What bacteria is used to check autoclave temperature?
Bacillus subtilis
Pressurized steam is
Used in an autoclave to sterilize a variety of objects
The prevacuum autoclave decreases:
cycle time
exposure of sensitive materials to steam
Can then heat up t o134C at 28-30lbs
Fractional sterilization is used for
Sterilization if materials are not suited to the autoclave
Heat to 100C for 30 min
Steam
AKA Tyndalization
Repeat at least 2 more times
Kills newly hatched spores on repeated reheating
Pasteurization reduces
bacterial populations in food and drink
This reduces the chances of spoilage and disease
Bacterial spores are not affected by pasteurization
Pasteurization temps
Holding method
: 62.9C for 30 min
Flash method
: 71.6C for 15 sec
Ultra
: 82C for 3 sec
Pasteurization Holding method
62.9C for 30 min
Pasteurization Flash method
71.6C for 15 sec
Pasteurization Ultra
82C for 3 sec
Hot oil
160C for 60 min
Doesn�t rust or dull instruments
Filtration
Traps Microorganisms
Uses porcelain, cellulose or ceramic
As fluid passes through a filter, organisms above a certain size threshold are trapped in the pores
Sand filtration is used for
Beer, water, pharmaceuticals
Cellulose acetate and polycarbonate filters are used to
Sterilize water
Trap bacteria
Air can be filtered using
A high-efficiency particulate air (HEPA) filter
Ultraviolet Light
265 wavelength is best to destroy DNA
Causes thymine molecules to link together
Errors in protein synthesis and impairment of chromosome replication occur
Doesn�t bend or go around corners
X rays and gamma rays (ionizing radiations)
Force electrons out of microbial molecules
Hard to control
More effective on G+
This affects cell metabolism and physiology
Used to control microbes in food
Drying food removes
The water necessary for microbes to live
Salting food causes
Water to diffuse out of organisms, causing dehydration and death
Low temperatures for food lowers
Microbial metabolic and growth rates, retarding spoilage
Antiseptics
Are used on living tissue
Disinfectants
Are used on non-living surfaces
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Author
tbednarick
ID
28366
Card Set
Microbiology Chatper 24 Microbial Control.txt
Description
Microbiology Chatper 24
Updated
2010-07-29T18:19:45Z
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