Molecular characterization of Bacillus cereus from milk and milk products

Abstract

Bacillus cereus is the major bacterial foodborne pathogens that cause various foodborne outbreaks worldwide. The occurrence of B. cereus in food environment is predominant and it has been characterized as both spoilage as well as pathogenic microorganism. In the present study, the incidence of B. cereus was investigated in a total of one fifty (150) samples (including raw milk, khoa, pasteurized milk and paneer) collected from different retail outlets in Chennai. The samples were screened for the presence of Bacillus cereus by conventional culture method on selective Mannitol egg yolk polymyxin (MYP) medium. The colonies were confirmed by their colony morphology, Gram’s staining and biochemical characterization. Microbial screening revealed predominance of Bacillus cereus. Further, all the culture positive colonies were subjected for PCR amplification by targeting Haemolysin (HL) gene. B. cereus was detected in 51/150 samples with an overall prevalence of 34%. Antibiotic susceptibility pattern revealed that the isolates were highly resistant to penicillin G (100%) and 100% sensitive to gentamicin, streptomycin, chloramphenicol, erythromycin and tetracycline. PCR positive samples were bulk produced, purified and sequenced and analyzed using DNA star sequence package. The BLAST analysis results revealed that Bacillus cereus isolates have 94% homology with the other Bacillus cereus isolates in the NCBI database. Thus in the present study revealed that, a relatively higher percent of the samples did not comply with the standard quality. Hence, the hygienic quality of milk and milk products need be improved considerably at different levels of processing to ensure food safety to the consumers.