Prevalence and characterisation of Bacillus cereus in cooked rice retailed in Ilara-Mokin, Nigeria

Bacillus cereus is widely distributed in different food products and causes a variety of symptoms associated with food poisoning. Rice has been suggested as a vehicle for contamination and being involved in B. cereus intoxication. Based on the aforementioned risks, studies of Bacillus cereus incidence along with its isolation and characterization are essential to establishing the safety of cooked rice. Using the selective culture technique, pure isolates of Bacillus cereus strains were characterized and identified based on cultural, and biochemical features. Characterization was done on the ability of the bacterial strains to hydrolyse casein and starch, ferment lactose, and lyse red blood cells (haemolysis). Out of the 47 samples screened, 45 isolates were detected in 14 samples. Antibiotic susceptibility testing revealed that all isolates showed resistance to Ampicillin (10 μg), but were susceptible to Erythromycin (15 μg), Vancomycin (30 μg), Tetracycline (30 μg), Ampicillin (10 μg), Gentamicin (10 μg), and Chloramphenicol (30 μg). 62.2%, 64.4%, 0% and 46.7% were capable of producing amylase, protease, ferment lactose and lyse red blood cells respectively. This study shows that 14 samples out of 47 samples of cooked rice in this work have the possible risk of foodborne infections/ intoxication that occurs as a result of the possibility of the development of B. cereus in favourable conditions and consumption of these products. Basically, prevention is by proper handling of raw materials, controlling the temperature of cooking and storing rice, and personal hygiene of food handlers.