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Staphylococcus aureus is a spherical bacterium (coccus) which typically appears in pairs, short chains, or bunched, grape-like clusters. These organisms are Gram-positive. The bacteria is capable of producing a heat-stable protein toxin that can cause illness.
Staphylococci can exist in air, dust, sewage, water, and food or on food equipment, environmental surfaces, humans, and animals. Humans and animals are the primary reservoirs. Staphylococci are present in the nasal passages and throats and on the hair and skin of 50 percent or more of healthy individuals. This incidence is even higher for those who associate with, or who come in contact with, sick individuals and hospital environments. Although food handlers are usually the main source of food contamination in food poisoning outbreaks, equipment and environmental surfaces can also be sources of contamination with staphylococcus.
Notably, foods that require considerable preparation (using hands), and are maintained at slightly elevated temperatures, are frequently associated with outbreaks. These foods typically include salads products (such as egg, tuna, chicken, potato, and macaroni) and bakery products (such as cream-filled pastries and cream pies). Other foods associated with outbreaks have included sandwich fillings, dairy products, meat products, poultry and egg products.
If Staphylococci are introduced into food, the bacteria can multiply and develop pre-formed enterotoxins. This usually occurs if the food is not kept hot enough (140°F or above) or cold enough (45°F or below). Once ingested, illness can be caused by the preformed enterotoxins. A toxin dose of less than 1.0 microgram in contaminated food, which is reached when the bacterial population exceeds 100,000 per gram, can produce symptoms.
The onset of symptoms in staphylococcal food poisoning is usually rapid and in many cases acute, depending on individual susceptibility to the toxin, the amount of contaminated food eaten, the amount of toxin in the food ingested, and the general health of the individual. The most common symptoms include nausea, vomiting, abdominal cramping and prostration. Some individuals may not always demonstrate all the symptoms associated with the illness. In more severe cases, headache, muscle cramping, and transient changes in blood pressure and pulse rate may occur. Recovery generally takes only two days.
As is true with most other common food-borne pathogens, the spread of Staphylococci to foods can be prevented by following good hygienic practices.