Staphylococcus aureus is a Gram-positive coccus. It is a non-motile, non-sporing and facultatively anaerobic.

Some strains of Staphylococcus aureus are capable of producing heat-stable toxins (enterotoxins) in food. It is the toxin which causes the typical symptoms associated with Staph. aureus food poisoning. No viable organisms of Staph. aureus need to be ingested, although, the organism needs to grow to levels of about 105 to 106/g food before the food becomes toxic. Typical symptoms are nausea and vomiting with occasional abdominal cramping and diarrhoea. Deaths have occurred amongst children and the elderly, but are rare.

Although Staph. aureus is a ubiquitous organism, the largest reservoir of enterotoxin producing staphylococci is man. Humans are an important source of Staph. aureus so the presence of staphylococci in cooked or processed foods can serve to indicate poor hygiene amongst food handlers. Animals may also act as a source of Staph. aureus , typically raw milk and raw meat (particularly pork) may be contaminated with the organism.

Foods involved in Staph. aureus food poisoning are typically those that have been handled and then temperature abused prior to consumption. Foods implicated in Staph. aureus food poisoning have been cooked meats (notably salted meat such as ham), poultry products, custard or cream-filled pastries, egg foods, cheese, prawns and salads containing potato.

Staphylococcus aureus can grow within the temperature range 7ºC - 48ºC, with an optimum of 35ºC - 37ºC. The limits for toxin production are, however, narrower than for growth, the optimum being between 40ºC and 45ºC (very little toxin is produced at the upper and lower extremes).

In most circumstances, Staph. aureus is not heat resistant and will be destroyed by pasteurisation. The toxin is, however, heat-stable, and has been known to survive a number of commercial sterilisation processes.

 

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