Growth and Survival of Staphylococcus aureus in Egyptian Domiati Cheese

Abstract

Domiati cheese was prepared from unsalted raw milk and from raw milk with 5 or 10% added sodium chloride, Milks were inoculated with enterotoxigenic Staphylococcus aureus strain 100 (produces enterotoxin A) before addition of salt and rennet. Cheeses were stored in whey containing 15% sodium chloride; were held at 30°C and were examined periodically for S. aureus count, aerobic plate count, DNase and moisture and salt contents. Numbers of S. aureus increased rapidly during preparation of cheese. There was a rapid decrease in number of viable S. aureus during storage of cheese made from unsalted milk and cheese made from milk with 5% added salt. In cheese from milk with 10% added salt, S. aureus survived until the fourth week. An increase in salt content and a decrease in the pH value of all cheeses occurred during storage in salted whey. DNase was detected only in cheese made from salted milk, but these samples did not contain a detectable amount of staphylococcal enterotoxin either after cheeses were made or after they were stored for 1 week.