Detection of toxigenic strains ofBacillus cereusin milk and dairy products through polymerase chain reaction

Abstract

Fifty nine samples of raw milk, 60 samples of pasteurized milk, 24 cream, 39 butter, 27 curd, 19 peda, 21 paneer and 20 skim milk powder samples were analyzed for the presence of different Bacillus species and a total of 182 isolates were obtained. The isolates were identified as Bacillus subtilis (51), Bacillus megaterium (39), Bacillus cereus (28), Bacillus licheniformis (32), Bacillus coagulans (7), Bacillus sphaericus (8), Bacillus pumilus (9) and Bacillus circulans (8). All the 28 Bacillus cereus isolates obtained in the study were subjected to polymerase chain reaction amplification for the presence of 365 nucleotides and all the isolates formed a distinct PCR product of 365 bp, which confirmed that these isolates were Bacillus cereus. Only 2 out of 28 Bacillus cereus isolates were found to be enterotoxigenic. One isolate harboured all the five genes of B, B’, L1, L2 and ET of the HBL-ET complex whereas the other isolate contained B, L1, L2 and ET genes and the B’ component was missing. Both the toxigenic strains of Bacillus cereus produced similar discontinuous haemolysis pattern on blood agar and cytotoxic effect on Vero cell line.