Prevalence of toxigenic traits in native food isolates of Bacillus cereus in the city of Mysore, Southern India

Abstract

In the growing concern for microbial food safety of traditional foods, the present study has attempted to characterize toxigenic profile of native food isolates ofBacillus cereus. In a total of 65 traditional foods, 26 isolates were characterized by morphological, cultural and biochemical attributes as B. cereus. Of these, 12 isolates (46%) were confirmed as B. cereus by PCR with 16S rDNA and phosphatidylinositol phospholipase C primers in PCR. Among B. cereus isolates, 8 (67%) and 6 (50%) were positive for binding and lytic components of haemolysin (hbl complex) and sphingomyelinase (sph) in PCR. Besides, 67% of the isolates exhibited discontinuous haemolytic pattern in blood agar. The toxigenic food isolates of B. cereus CFR 1529, 1530, 1534 and 1536 revealed a high degree of sequence homology with selected strains of B. cereus and other species of B. cereus cluster as evidenced in sequence homology of partial nucleotide sequences of respective PCR amplicons of selected target genes. The study does indicate that toxigenic traits appear to be well spread within B. cereus cluster and have become stable traits among food isolates of B. cereus prevalent in the food chain. Key words: Bacillus cereus, PCR, phosphatidylinositol phospholipase C, haemolysin BL, sphingomyelinase, toxigenic, sequence homology, microbial diversity.