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

28366

Card Set

Microbiology Chatper 24 Microbial Control.txt

Description

Microbiology Chatper 24

Updated

2010-07-29T18:19:45Z

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