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P3-114 A Study to Assess the Numbers and Prevalence of Bacillus cereus and Its Toxins in Pasteurized Fluid Milk

Wednesday, July 12, 2017
Exhibit Hall (Tampa Convention Center)
Saleema Saleh-Lakha , AFL, University of Guelph , Guelph , Canada
Carlos Leon-Velarde , AFL, University of Guelph , Guelph , Canada
Shu Chen , AFL, University of Guelph , Guelph , Canada
Susan Lee , University of Guelph , Guelph , Canada
Kelly Shannon , University of Guelph , Guelph , Canada
Martha Fabri , Ontario Ministry of Agriculture, Food and Rural Affairs , Guelph , Canada
Bruce Keown , Ontario Ministry of Agriculture, Food and Rural Affairs , Guelph , Canada
Gavin Downing , Ontario Ministry of Agriculture, Food and Rural Affairs , Guelph , Canada
Introduction: Bacillus cereus is a pathogenic adulterant of raw milk and can persist as spores and grow in pasteurized milk. Foodborne outbreaks attributed to B. cereus toxins may be under-reported due to short duration of the illness and potential misdiagnosis with diseases caused by Staphylococcus aureus or Clostridium perfringens.

Purpose: The objectives of this study were to determine the prevalence of B. cereus and its enterotoxins in pasteurized milk at its best-before date and to conduct toxigenic characterization of B. cereus isolated from milk.

Methods: Bacillus cereus counts in milk samples (n = 254) stored at 4°C, 7°C, and 10°C were estimated according to MFLP-42, "Isolation and Enumeration of the Bacillus cereus group in Foods". Samples containing >104cfu B. cereus/ml were analyzed for the presence of enterotoxins using the 3M™ TECRA™ Bacillus Diarrhoeal Enterotoxin Immunoassay. Bacillus cereus isolates obtained from milk were analyzed for the presence of toxin genes nheA, entFM, hblC, cytK and CER via multiplex PCR.

Results: Over 5.5% of moderately temperature-abused products (stored at 7oC) were found to contain >105 cfu B. cereus/ml and 4% contained enterotoxins. Over 31% of products contained >105 cfu of B. cereus/ml and associated enterotoxins when stored at 10oC. Enterotoxin production by B. cereus in pasteurized milk started at 7-8 days of 7°C storage. Characterization of 17 representative B. cereus isolates from pasteurized milk revealed five toxigenic gene patterns, with all of the strains carrying genes encoding for diarrhoeal toxins, but not for an emetic toxin. One of the strains contained all four diarrhoeal enterotoxin genes (nheA, entFM, hblC, and cytK).

Significance: The results of this study demonstrated the risks associated with moderately temperature-abused, pasteurized milk and the necessity of a controlled cold chain throughout the shelf life of fluid milk in order to enhance product safety and minimize foodborne illness.

Back to: Poster Session 3 – Low-water Activity Foods, Packaging, Produce, Microbial Food Spoilage, Antimicrobials, Laboratory and Detection Methods, Water
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