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Control of microbial growth
Effected in two basic ways:
-

Killing microorganisms and Inhibiting microbial growth

Involves the use of: Physical/Chemical agents that kill or prevent growth
Principles of microbial control
-

Prevention → Control of growth to prevent infection

-

Sterilization → Complete destruction
- No ‘levels’ of sterilization → All or Nothing
- Utilizes; Heat, Radiation, Some chemicals and Physical removal

Disinfection → reducing growth on non-living surfaces
-

(Organic matter interferes with heat treatments and chemical control agents)

Antisepsis → reducing growth on living tissue
Physical Methods
Heat

Most frequent and widely used
1
...
Time of Application
3
...
Fresh or cooked foods are flash frozen
2
...
Foods are sealed in moisture and oxygen free packaging
4
...
s
...
for 30 min kills everything

Moist Heat, Pasteurization

Denatures proteins

Kills pathogens in food products

Dry Heat, Flaming

Incineration of contaminants

Used for inoculating loop

Dry Heat, Hot air oven

Oxidation & Denatures proteins

170°C for 2 hours; Used for glassware & instrument sterilization

Filtration

Separation of bacteria from liquid
(HEPA: from air)

Used for heat sensitive liquids

Cold, Lyophilization (also
desiccation)

Desiccation and low temperature

Used for food & drug preservation; Does not necessarily kill so
used for Long-term storage of bacterial cultures

Cold, Refrigeration

Decreased chemical reaction rate

Bacteriostatic

Osmotic Pressure,
Addition of salt or sugar

Plasmolysis of contaminants

Used in food preservation (less effective against fungi)

Radiation, UV

DNA damage (thymine dimers)

Limited penetration

Radiation, X-rays

DNA damage

Used for sterilizing medical supplies

Strong vis
...
Less effect on appearance and texture
Controversy
...
Effective against
Aerobic bacteria (not
obligate/facultative anaerobes)

Bind to bacterial 30S ribosomal
subunit (some work by binding
to the 50S subunit)

Lincomycin
Gram-

Aminoglycosides

Streptomycin,
Tobramycin
Gentamicin

Bacterial
type

Antibiotic Class

Example

Microorganisms

Mechanism of action

Gram+/-

Tetracyclines

Tetracycline

Syphilis, chlamydia, Lyme disease, mycoplasmal infections,
rickettsia

Broad spectrum, inhibit protein
synthesis at 30S subunit

Efficient against Gram+

Disrupt the synthesis of the
peptidoglycan layer of bacterial cell
walls
...

The greater the diameter of the zone, the higher the efficacy of the antibiotic
Antibiotic resistance
-

Growing Problem
Indiscriminant and inappropriate use
Super Bugs: Methicillin Resistant S
...
tuberculosis



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