Enterotoxigenic profile of Bacillus cereus strains isolated from raw and pasteurized milk

The present investigation was undertaken to study the incidence of Bacillus cereus in milk, its source of contamination and to detect the enterotoxigenic genes (hblCDA, nheABC, cytK and entFM) in isolates by a multiplex-PCR. B. cereus could be isolated from 2 (4%) of the 50 raw milk samples taken aseptically directly from the animals, while among 36 raw pooled milk samples from dairy farms and 74 pasteurized milk samples, 12 (33.33%) and 28 (37.83%) turned out positive, respectively. The levels of B. cereus in contaminated milk samples ranged from 0.5×102 to 2.6×105 CFU/ml. The other related Bacilli like B. mycoides and B. thuringiensis were isolated from 10 (6.25%) and 6 (3.75%) milk samples, respectively. The multiplex-PCR of B. cereus isolates revealed the incidence of various enterotoxigenic genes hblD, hblA, hblC, nheA, nheB, nheC, cytK and entFM as 73.80, 69.04, 71.42, 95.23, 90.45, 95.23, 66.7 and 100%, respectively. A higher incidence of B. cereus in pasteurized milk and a large proportion (54.76%) of isolates harbouring all the enterotoxigenc genes, most of them being among the isolates from pasteurized milk samples (73.91%) pose a potential public health threat. Moreover, the genes in the operons (hblCDA and nheABC) can occur independently from each other.