Occurrence and characterization of toxigenic Bacillus cereus in food and infant feces

ABSTRACT

Objective:To investigate the true incidence of Bacillus cereus (B. cereus) in food and children diarrhea cases. Methods:A total of 110 samples of various dairy products such as raw milk, long life pasteurized milk, yoghurt and infant powdered milk formulas, raw rice, and feces were examined for the presence of B. cereus by selective plating on mannitol-egg-yolk-polymyxin agar. Confirmation of B. cereus was carried out by biochemical tests and PCR. Identification of non-B. cereus isolates was carried out by 16S rDNA sequencing. Antimicrobial susceptibility was done by disk diffusion method. Results:Overall 35 samples (31.8%, n=110) yielded Bacillus-like growth. Of which 19 samples (54.28%) were positive for B. cereus. All isolates were positive for enterotoxin production. No psychrotolerant B. cereus strains were detected in all samples. All B. cereus isolates were resistant to penicillin G, but susceptible to vancomycin, erythromycin and clindamycin. Conclusions:The results of this study confirm the importance of including B. cereus in disease control and prevention programs, as well as in routine clinical and food quality control laboratories in both Saudi Arabia and Egypt.