Food Safety

Overall informations on the Microbes

Listeria Monocytogenes

A Gram- positive bacterium

Illness: Listeriosis

Sources: raw milk, ice cream, raw vegetables, raw meat, raw and smoked fish. Its abiliity to grow at temperature as low as 3°C permits multiplication in refrigerated foods.

Favourable conditions
- grow under aerobic and anaerobic conditions
- able to grow @ refrigeration temperatures (to 1°C; 34°F)
- low pH (<4.6) prevents growth of organisms
- withstands repeated freezing and thawing
- survives for prolonged periods in dry conditions
- low aW of 0.90 @ 30°C control growth of organisms.



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Clostridium Botulism

an anaerobic, gram-positive, spore-forming rod that produces a potent neurotoxin

spores are heat-resistant and can survive in foods that are incoorectly or minimally processed.

Illness: Botulism

Sources: chicken, green beans, canned food etc; Almost any type of food that is not very acidic (pH above 4.6)

Favourable conditions
- organisms grow best under anaerobic/reduced oxygen conditions. Non-proteolytic types can grow @ low temperature (to 3°C; 37°F). Most proteolytic types can grow to 10°C.
- low pH and low aW control the growth.



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Salmonella spp.

non-sporeforming and graw-negative.

Illness: Salmonellosis

Sources: raw meats, poultry, eggs, milk and dairy pdts, fish etc

Favourable condition
- will be killed by mild heat (above 60°C)
- grows under aerobic and anaerobic conditions. Grow in temperature range of 5.2 to 47°C. Optimum temperature for growth is 35 to 37°C.
- low pH (<4.6) prevents growth. Optimum pH: 6.5 to 7.5



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Staphylococcus aureus

Gram-positive

Illness: Staphylococcal food poisoning

Sources: Poultry and egg products, salads, chicken etc

Favourable condition
- killed by mild heat (above 60°C)
- grows in either aerobic or anaerobic conditions. Temperature growth range is 6.7 to 45.4°C. Optimum growth temperature is 37 to 40°C.
- pH growth range 4.5 to 9.3.
- organisms resistant to high salt (up to 15%)



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Bacillus cereus and other Bacillus spp.

gram-positive, facultatively aerobic sporeformer

Illness: food posioning

Sources: meats, milk, vegetables, rices products, starchy food such as potato, pasta etc

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