Growth abilities and enterotoxin production of Staphylococcus aureus strains in herby cheese

Staphylococcus aureus reference strains, producing A, B, C, and D enterotoxins, were individually or as mixture inoculated at the rate of 10(5) cfu/mL into 10 herby cheese samples, experimentally produced from pasteurised or raw milk. The growth rates and enterotoxin production abilities of the strains were examined during the 90 d ripening period. During the ripening, S. aureus, aerobic mesophilic and lactic acid bacteria, a(w), pH, acidity, salt levels, and A, 13, C, and D enterotoxins were examined at 11 different periods. The level of S. aureus in cheese samples produced from pasteurised milk decreased regularly after 15 d, and on the 90(th) d was reduced to log 2 cfu/g. In cheese made from raw milk, the S. aureus levels at the beginning of the ripening period increased up to 107 cfu/g, and then decreased to the starting level on the 90(th) d of the ripening. Throughout the ripening period, enterotoxin A was observed in the curd stage in pasteurised cheese samples inoculated individually with toxin A producing strain. Enterotoxins A, B, C, and D were observed on the third day in pasteurised mixed cheese inoculated with the mixture of S. aureus strains. Enterotoxin C was observed in cheese inoculated with toxin C producing strain on the 15(th) d. No enterotoxin was observed in cheese samples made from the raw milk during the processing until the end of the ripening period, and the pH levels did not drop compared to those of pasteurised cheeses.