Distribution Characteristics of Antimicrobial-Resistance and Virulence-Associated Genes of Bacillus cereus in Animal-Origin Food in Guangzhou, China

This study investigated the prevalence and genomic characteristics of Bacillus cereus group organisms in animal-origin foods sold in Guangzhou, China. A total of 505 retail samples, including 117 milk samples and 388 commercially available smoked sausage products, were collected from supermarkets and farmers’ markets. The isolation rates of B. cereus group organisms were 8.5% in milk and 44.9% in smoked sausages. Whole-genome sequencing of 169 isolates showed that antimicrobial-resistance genes, including bacII, fosB and vanZF, and diarrheal virulence-associated genes, including nheA, nheB and nheC, were widely distributed among the isolates. Most representative isolates showed biofilm-forming ability, and three antimicrobial-resistant isolates carrying multiple virulence-associated genes showed pathogenic potential in mice under high-dose experimental administration. These findings indicate that retail smoked sausage products can serve as a reservoir of B. cereus group organisms with antimicrobial-resistance, virulence-associated and biofilm-forming traits. However, the detection of resistance- or virulence-associated genes does not necessarily prove gene expression, toxin production, phenotypic resistance or consumer exposure risk. This study did not directly evaluate growth of B. cereus in sausage matrices during storage. Therefore, the present results indicate a potential microbiological hazard rather than a quantified consumer risk. Product-specific challenge studies under defined storage conditions are required to determine whether B. cereus can proliferate in particular sausage products and reach hazardous levels at consumption.