Bacillus cereus is an important foodborne pathogen, which can cause severe food poisoning. The aim of this study was (i) to evaluate the quantitative prevalence of B. cereus in retail prepackaged infant formula and ready-to-eat rice flour in China and (ii) to gain the basic information on pheno- and genotypic characteristics of B. cereus isolates. We found that 40 out of the 587 samples were positive for B. cereus. B. cereus in 3.5% of infant formula samples and 1.0% of rice flour samples outnumbered 100 Colony-Forming Units (CFU)/g. B. cereus level even attained 103-104 CFU/g in four infant formula samples and one rice flour sample. Furthermore, we identified the distribution patterns of toxin genes in B. cereus isolates. The results showed that 97.5% of B. cereus isolates harbored at least one enterotoxin gene. Antibiotic susceptibility tests revealed that all isolated B. cereus strains were resistant to penicillin and 50% of them were multidrug resistant. Thirteen new sequence types (STs) and four new alleles were identified via multilocus sequence typing. Clonal Complex (CC) ST-205 and CC ST-142 were predominant clonal complexes. Interestingly, we revealed the special relationship between STs of B. cereus isolates and the geographical distributions of infant food manufacturers for the first time. The data implied that B. cereus of different STs might have a distinct ecological niche in China. In view of relatively high contamination level of enterotoxin- producing B. cereus in a proportion of infant foods, especially in those suitable for the ≤6-month-old infant group, appropriate safety criteria and hygienic control measures for infant foods should be drafted in China to prevent B. cereus infection.
Keywords: Bacillus cereus; antibiotic susceptibility; infant foods; multi-locus sequence typing (MLST).