Enterotoxigenic profile, biofilm production, and antimicrobial resistance of Bacillus cereus isolated from rice-based food marketed in southern Mexico

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Bacillus cereus is responsible for food poisoning worldwide; thus, the characterization of strains isolated from food, in this case rice, is essential. The objective of this study was to identify the toxigenic profile, lytic enzymes, antimicrobial resistance, and biofilm production of B. cereus strains isolated from rice. The genetic profile of toxins and biofilm-related genes in the strains was determined by endpoint PCR. Biofilm formation was visualized using safranin staining, and the evaluation of lytic enzymes was conducted in culture media. Psychrophilic characteristics were monitored by assessing the growth of the strains at refrigeration temperature. The GTG5 technique was employed to determine the genetic diversity of the strains, and their antimicrobial resistance was validated through minimum inhibitory concentration testing. The strains of B. cereus s.l. isolated from rice contained genes for enterotoxins and genes associated with biofilm production. However, the strains did not possess the cereulide gene. The strain isolated from fried rice was the only one that contained the hbl toxin gene and the eps2 operon. Interestingly, this strain was the only one that did not produce biofilm. It exhibited intermediate sensitivity to erythromycin, was positive for amylase activity, showed high lecithinase activity, and was capable of growing at refrigeration temperature.