Camembert cheese was made from pasteurized milk inoculated to contain, per milliliter, approximately 100 cells of enteropathogenic strains of Echerichia coli. A Most Probable Number technique was used to enumerate E. coli at intervals during manufacture and ripening of the cheese. Identity of isolates obtained was determined serologically. Growth of E. coli was minimal until after curd was cut and hooped. Rapid growth ensued and populations in excess of 104/g appeared in some Cheeses 5 h after the Cheesemaking process began. Overnight storage of Cheese in hoops was accompanied by a decline in numbers of viable E. coli. This coincided with a drop in pH of the Cheese to 5.0 or below. Salting of cheese and 1 day of ripening at 15.6 C ( 60 F) caused a further decline in number of viable E. coli. This decline continued during the rest of the week at 15.6 C ( 60 F) and during storage at 10 C (50 F). From 0 to 9 weeks at 10 C (50 F) were required before cheese was free of viable E. coli. Substitution of Streptococcus cremoris C1 for a commercial lactic starter culture favored survival of E. coli so that 9-week old Cheese contained >104/g. When cheese was made from milk that contained penicillin, the E. coli population was approximately 109/g in 24-h old cheese and 107/g when the Cheese was 9 weeks old.
1Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison and by contributions from the food industry to the Food Research Institute.
2Present address: Cheese Division, Borden Foods, Plymouth, Wisconsin 53073.