Prevalence and characterization of Bacillus cereus isolates from clinical and natural sources

Bacillus cereus clinical isolates recovered from blood, wounds and diarrheal feces as well as natural isolates from normal feces, rice, dehydrated milk, and soil were characterized with respect to their biochemical profiles, antimicrobial susceptibility and enterotoxigenicity. The biochemical profiles of all the isolates were similar regardless of their sources. However, some degree of variability was shown in the Voges-Proskauer, nitrate reduction, and esculin hydrolysis tests and in the ability to grow in the presence of 40% bile. All the isolates were resistant to amoxicillin, oxacillin, and penicillin and susceptible to gentamicin and vancomycin. Susceptibility to cephalothin was variable among the clinical isolates, whereas susceptibility to clindamycin and erythromycin was inconsistent for all of them. The B. cereus clinical isolates recovered from human diarrheal feces were found to be strong producers of diarrheal enterotoxin as revealed by induction of diarrhea in mice and vascular permeability reaction. The clinical isolates recovered from wounds and blood and the natural isolates recovered from rice, milk, and normal feces, on the other hand, were weak producers of diarrheal enterotoxin.