Staphylococcus Aureus

Staphylococcus aureus


S.aureus is a gram positive coccus, which appears as grape-like clusters when viewed through a microscope and has large, round, golden-yellow colonies, S.aureus is a commensal of warm blooded animals (Commensal bacteria are normal bacteria which make up part of the mucosal flora (i.e. the mouth, the nose, the lungs, and the gastrointestinal and urogenital tracts) of animals but do not cause disease.)

S.aureus can produce a range of substances including enterotoxins (toxin produced by bacteria that is specific for intestinal cells and causes the vomiting and diarrhoea associated with food poisoning) and haemolysins (the destruction of red blood cells with release of haemoglobin

Food poisoning occurs when the growth of S.aureus in a food reaches about 1 million (106 cfu/g) and toxins have formed in the food.

Contamination of food with S.aureus/S.aureus toxin is usually caused by food handlers. Can be a result of poor handling techniques or such as a food handler with open sores, spots or lesions.

Symptoms occur within 1 to 8 hours after ingestion of the contaminated food.

Symptoms include nausea, vomiting and abdominal cramps

Usually self limiting and clears up without any specific treatment

Staphylococcal food poisoning is not an infection, but an intoxication that results from ingestion of staphylococcal enterotoxins in food. The enterotoxins are produced when food contaminated with S. aureus is improperly stored under conditions that allow the bacteria to grow. Although contamination can originate from animals or the environment, food handlers with poor hygiene are the usual source. Effective methods for preventing staphylococcal food poisoning are aimed at eliminating contamination through common hygiene practices, such as wearing gloves, and proper food storage to minimize toxin production.

S.aureus is resistant to drying which makes it difficult to control (eg hand washing and drying not always effective)

S.aureus can colonise on equipment if it is left wet (and biofilms may also occur will protect the organism even more)

S.aureus is quickly destroyed by adequate cooking but if enterotoxins have already formed, these can be resistant to heat.

S.aureus are able to grow and produce enterotoxin in low water activity foods
environment is another source of contamination

S.aureus are resistant to freezing and thawing. The enterotoxin is not affected by freezing (problems with ice cream).

Heat resistance is increased in high fat and dry foods, so increased cooking requirements must be put into place when preparing theses type of products.

They are tolerant to salt (can cause a problem with foods such as cooked hams, etc)

They can grow in acidic conditions (pH <4.3)

Can grow aerobic and anaerobically