Staphylococci in Colby Cheese

Colby cheese was manufactured from raw milk inoculated with a coagulase-positive Staphylococcus aureus and from noninoculated raw milk obtained from cows with subclinical mastitis. Organisms were enumerated on plate count agar (PCA) and on Staphylococcus Medium No. 110 (S-l]0) on samples of milk, curd, and whey taken during the cheese-making process and on samples of cheese taken at 15-day intervals during storage for 4 mo. at 10 C. Many representative colonies were picked from S-110 medium and examined for coagulase reaction.