The Growth and Survival of Streptococcus Faecalis in Pasteurized Milk American Cheddar Cheese

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Abstract
Three lots of milk pasteurized at 143-145[degree]F for 30 min. were made into American Cheddar cheese. These lots contained, respectively, 2% commercial lactic starter; 1% commercial lactic starter plus 1% S. faecalis starter; and 2% S. faecalis starter. A selective penicillin-azide medium was used to count and isolate the enterococci. In 1-day-old cheese made with commercial lactic starter the number of bacteria growing on the selective medium was small, 300 per ml., but these gradually increased to 23 million per ml. at the end of 120 days at 50[degree]F, and to 28 million per ml. after 120 days at 60[degree]F. At the end of 180 days the counts on the selective medium had decreased to 11 million and 13 million per ml. at 50[degree] and 60 [degree]F, respec- . tively. In this cheese most of the increase was due to lacto-bacilli and not to enterococci. When S. faecalis was used as a starter for pasteurized milk American Cheddar cheese, the highest enterococcus count was found to exist in the cheese curds just prior to salting, this count being 500 million per g. for cheese containing 1% commercial lactic starter plus 1 per cent S. faecalis starter, and 1370 million per g. for the cheese containing 2% S. faecalis starter. S. faecalis grows and survives in Cheddar cheese in large numbers for a considerable period of time, both at 50[degree] and at 60 [degree]F. At 50 [degree]F, cheese made with both lactic and 5. faecalis starters still gave counts of 345 million per g., and cheese made with S. faecalis starter gave counts of 1085 million per g. at the end of 60 days, whereas at 60 [degree]F the former cheese contained 305 million per g. and the latter cheese contained 750 million per g. at the end of 60 days. At the end of 180 days the number of bacteria in the cheese growing on the selective medium had decreased, although a large number was still present.

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