Virulence and recovery of Staphylococcus aureus relevant to the food industry using improvements on traditional approaches

Staphylococcus aureus is found in a wide variety of habitats, including human skin, where many strains are commensals that may be clinically significant or contaminants of food. A number of factors contribute to the virulence of S. aureus, including deoxyribonuclease (DNase), catalase, lipases, and hemolysins. However, the most notable virulence factors are the enterotoxins. Staphylococcal food poisoning results from consumption of one or more preformed enterotoxins resulting in symptoms of intoxication. In clinical and food settings, S. aureus is found within a high density of other microflora, requiring selective bacteriological media for isolation and enumeration. However, due to sublethal stress placed on food contaminants, including S. aureus during processing, direct detection/enumeration using selective media may underestimate the level of contamination. One option for recovering sublethally injured organisms is an approach using selective agar overlays, a method shown to be effective for coliforms and other common pathogens. This inexpensive variation on the common standard plate count means for enumeration of bacteria in food improves detection sensitivity for cells that may be sublethally injured or stressed from food processing treatments. Therefore, implementation of this as a means for more accurately determining the microbiological quality of foods is met with low cost and general acceptance for smaller food processing operations. The application of this technique, however, has not been largely explored for specific Gram-positive pathogens such as S. aureus, but is perhaps warranted owing to the increasing number of characterized enterotoxins from these strains.