Salmonella typhimurium Phage-Type 10 from Cheddar Cheese Implicated in a Major Canadian Foodborne Outbreak

Abstract

Levels of Salmonella typhimurium phage-type 10 in Cheddar cheese implicated in a major Canadian foodborne outbreak ranged from 0.36 to 9.3 salmonellae/100 g. Such a low level contamination likely accounted for the uneven distribution of the organism among subsamples of individual lots. Coliform and Escherichia coli counts were within acceptable limits, whereas three of the 11 lots tested contained ≥105 Staphylococcus aureus per gram but no staphylococcal enterotoxins. Campylobacter and Yersinia spp. were not detected in any of the 12 lots examined. Ability of S. typhimurium to survive up to 8 months in Cheddar cheese stored at refrigerator temperature (5°C) underlines the inadequacy of current regulations requiring a 60-d storage of cheese manufactured from heat-treated (unpasteurized) milk before sale. Results underlined the greater sensitivity of selective enrichment in tetrathionate brilliant green (43°C) than in selenite cystine (35°C) for detection of Salmonella in cheese.