Antibiotic susceptibility and selected toxin genes profiles among Bacillus cereus isolated from raw bovine milk from a milk collection center in Kawempe Division, Kampala District

Abstract

Bacillus cereus causes food intoxication hence a burden to public health. Bacillus cereus is also among the top five foodborne pathogens, especially in starchy foods and raw cow milk. The pathogenicity of the B. cereus is associated with the potential to produce diarrheal and emetic toxins. The pathogen has been associated with clinical infections, whose management could be challenged by antimicrobial resistance. There is scanty information on the contamination levels of raw bovine milk with B. cereus, its toxigenic potential, and its susceptibility to antibiotics in Uganda. This study aimed to determine the proportion of raw bovine milk contaminated with B. cereus sold within Kawempe division, Kampala as well as its toxigenic potential and antibiotic susceptibility profiles. In the present study, 30 raw bovine milk samples were collected from a milk collection centre in the Kawempe division, Kampala . From the samples where growth occurred, five isolates were selected for further characterization. Isolates were identified and confirmed using gram-staining, citrate, catalase, oxidase and motility. Antibiotic susceptibility profiles were determined by the Kirby-Bauer technique, while multiplex real-time PCR allowed the detection of toxigenic genes (hblD, nheA, cytK 1 and ces). Of the 30 milk samples, eight (26.7%) were contaminated with B. cereus. All the 40 isolates that were selected for antibiotic sensitivity testing, exhibited susceptibility to gentamycin, tetracycline, chloramphenicol and ciprofloxacin, but all were resistant to ß-lactam products including Ampicillin and Penicillin. The hblD, nheA, cytK1 and ces were encountered in 82.5 % (33/40), 85 % (34/40), 0%, and 0% of the B. cereus isolates respectively. Contamination of milk with B. cereus and the presence of the diarrheal toxin genes, hblD and nheA, implies that there is a potential risk of associated food-borne illnesses, especially where raw bovine milk is consumed. The cytK1, a diarrheal toxin-encoding gene was absent. In this research, the ces was absent hence no potential for emesis. Thus, there is a need for wider surveillance of contamination of especially the raw bovine milk.