Source and Persistence of Salmonella muenster in Naturally Contaminated Cheddar Cheese

Public health authorities in Oxford, Middlesex and Elgin Counties, Ontario, seized raw milk Cheddar cheese due to presence of Salmonella muenster. Investigations by these units and the University of Guelph traced the source of Salmonella to one particular milk supplier shipping to a cheese factory. Analysis of milk samples from a herd of 35 cattle revealed only one cow shedding S. muenster directly into the milk (ca. 200 CFU/ml). Eleven of 181 vats of cheese, produced at the factory between May and October 1982, were positive for Salmonella at the curd stage. Only 2 vats of the finished raw milk Cheddar, however, were positive. One lot of Salmonella-positive cheese was still positive after the legally required 60-d holding period and remained so for 125 d.