Survival and growth of food poisoning bacteria following inoculation into cottage cheese varieties

Following inoculation into cottage cheese varieties with and without sorbic acid, obtained directly from the manufacturer, strains of enteropathogenic Escherichia coli and other E. coli survived but failed to multiply during storage at 7, 10 or 25 degrees C. In the absence of sorbic acid spoilage due to Pseudomonas fluorescens occurred after storage for 5-13 days at 7 or 10 degrees C and 1-2 days at 25 degrees C. Salmonella enteritidis, S. hadar, S. saint-paul, S. typhimurium and S. virchow survived but failed to multiply at 10 degrees C and, in the case of most strains, at 20 or 25 degrees C. S. typhimurium multiplied 100-fold in one batch of cottage cheese with peppers and onion in the absence of sorbic acid during storage at 25 degrees C for 2 days; spoilage of this batch occurred due to yeasts or yeasts and moulds after storage for 4-8 days at 10 degrees C and 0-2 days at 20 or 25 degrees C. Following inoculation into cottage cheese varieties, prepared in the laboratory and which did not contain sorbic acid, as contaminants of the added protein or vegetable ingredients the numbers of Staphylococcus aureus declined during storage at 10 and 20 degrees C, the numbers of Bacillus cereus and S. typhimurium increased at both temperatures, and the numbers of Yersinia enterocolitica increased at 10 degrees C, but declined at 20 degrees C. Spoilage occurred due to the growth of moulds and P. fluorescens after storage for 5-14 days at 10 degrees C, and due to P. fluorescens after storage for up to 2 days at 20 degrees C. In products inoculated in a similar way but which contained sorbic acid (500-530 mg/kg), the numbers of S. aureus and B. cereus declined and in most products the numbers of S. typhimurium and Y. enterocolitica remained constant. In cottage cheese with chicken, however, the numbers of Y. enterocolitica increased 100-fold during storage of the product for 14 days at 10 degrees and the numbers of S. typhimurium increased 100-fold during storage for 2 days at 20 degrees C. Spoilage of this product due to P. fluorescens occurred after storage for 8-14 days at 10 degrees C, but was not evident at 20 degrees C after 2 days.