Microbial Control Chpt 7 Physical Methods

Microbial Control Chapter 7

Physical Methods
I Disinfection: for inanimate objects. Reduces the amount of bacteria. (decreases, not eliminate)
II Sterilization: for animate objects. Kills all cells.
A. cidal: kills bacteria and endospores
B. static: upon usage killed, but when removed they regrow. (refrigeration)
C. order of death:
1. gram +
2. lipid virus
3. gram –
4. endospore
III Heat: structural proteins and enzymes damaged (denatured). Water is lost.
A. Dry heat: kills all forms of life.
1. hot air: 2 hours at 170 C. (baking) requires a long time.
2. direct flame/incineration
B. Moist heat
1. boiling: 10 minutes at 100 C. Used for food and water.
a. Will not kill Clostridium.
b. Kills 95% of bacteria.
c. for disinfection of food and water.
2. autoclaving: 15psi @ 121 C for 20 minutes.
a. kills all organisms and spores
b. widely used in medical applications.
3. Pasteurization: 15 seconds @ 72 C
a. milder process
b. makes materials (wine, milk) safe
c. aka: intermediated (intermittent) heating
4. UHT (ultra high temperature) 5 seconds @ 140 C
a. short time at high temp
b. “flash” sterilization
c. Ex: start at 74 C, heat at 5 seconds @ 140 C, back to 74 C.
IV Filtration
A. Membrane filters for fluids
B. HEPA filters for air
V Radiation
A. Ionizing radiation (x-ray, gamma ray)
1. highly penetrating
2. generate free radicals inside cells
3. used for certain medical products
4. use on food being explored. (don’t want humans creating free radicals)
B. Non-ionizing radiation (UV)
1. damages DNA
2. poor penetration
3. used primarily for surface sterilization (germicidal lamps)
VI Drying: creates a hypertonic situation
A. Salting
B. Sugaring
VII Low Temperature
A. Refrigeration is bacteriostatic

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Various notes

Microwaving does not kill endospores

Antibiotics are ingested to kill bacteria.

Clostridium = endospores

Order of death:
1. gram +
2. lipid virus (b/c easily soluble in disinfectant)
3. gram - (b/c of polylipid layer)
4. endospore