The occurrence of Bacillus cereus in Danish pasteurized milk

Four hundred and fifty eight samples of pasteurized full fat milk, pasteurized low fat milk (1.5% milk fat) and pasteurized double cream were collected from three Danish dairies (A, B and C) over a period of 1 year. The milk samples were stored at 7 ± 0.5 °C for 8 days, and were then examined for the presence of Bacillus cereus and other aerobic mesophilic microorganisms. In addition, 115 raw milk samples taken from weighing tanks at the three dairies were examined for psychrotrophic B. cereus. B. cereus was isolated from 257 (56%) of the 458 pasteurized milk samples examined, and no differences between full fat milk, low fat milk and double cream were observed as regards the percentage of B. cereus positive samples. However, the mean count of B. cereus was significantly higher in double cream than in the other products. No significant differences was observed between the dairies. The prevalence of B. cereus in pasteurized milk products during summer and winter was 72 and 28%, respectively, and the mean counts of B. cereus was significantly higher during summer as well. Psychrotrophic B. cereus was detected in 29 of 115 samples of raw milk (25%). In 120 of the 257 samples of pasteurized milk found to be positive, the viable count of B. cereus obtained was in the range between 103 and 3 × 105 cfu/ml.