Behavior of Virulent Yersinia enterocolitica During Manufacture and Storage of Colby-like Cheese.

The ability of Yersinia enterocolitica to grow and survive during manufacture and storage of Colby-like cheese was determined. Pasteurized whole milk artificially contaminated with two virulent strains of Y. enterocolitica (separately) was used to make cheese. Y. enterocolitica was enumerated by surface-plating of samples on Cefsulodin-Irgasan-Novobiocin (CIN) agar. Y. enterocolitica increased 1000-fold, to about 1 × 10/g of curd, during the manufacturing process. After this point, numbers of Y. enterocolitica in cheeses generally decreased over a period of weeks. One strain could not be detected in cheese after 7 weeks at 3 ± 1°C. However, the other strain persisted at numbers in excess of 200/g after 8 weeks at the same temperature.