Staphylococci exist in air, dust, sewage, water, milk 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. A wide range of foods maybe involved in Staphylococcal food poisoning including ham, turkey, chicken and chicken salad, baked products, especially filled pastries, table ready-meats (sausage etc.), precooked frozen foods and dairy products.
S. aureus cells are relatively more resistant than many gram negative food spoilage organisms. Human intoxication is caused by ingesting enterotoxins produced in food by strains of S. aureus, usually because the food has not been kept hot enough (60ºC, or above) or cold enough (7.2ºC, or below). In frozen foods they may survive even at -10ºC. In general, survival of S. aureus is best in foods that contain high concentration of sugars, eggs and buffering component such as phosphates and protein. Salt concentration less than 9.5%, temperature more than 20ºC and a pH in the range 6-8 are favourable for growth and enterotoxin formation.