Genotyping, Antimicrobial Susceptibility and Biofilm Formation of Bacillus cereus Isolated from Powdered Food Products in China

This study was conducted to reveal the genotyping, antimicrobial susceptibility, and biofilm formation of isolated from powdered food products in China. Five hundred powdered food samples were collected from five provinces in China: 100 samples each of powdered infant formula (PIF), soy milk powder (SMP), lotus root powder (LRP), walnut powder (WP), and rice flour (RF). The genotyping of isolates was analyzed using multilocus sequence typing; meanwhile, antimicrobial susceptibility, and ability of biofilms formation on stainless steel tube of isolates were evaluated. Forty-two strains were detected with an overall contamination rate of 8.4%, as well as, the highest contamination rate was found in SMP (10%), followed by LRP (9%), WP (9%), RF (8%), and PIF (6%). These isolates were divided into 22 sequence types (STs); among them, ST32 (4/42, 9.5%) was the predominant ST. Phylogenetic relationships showed that the 42 strains of were divided into three groups (group I, group II, and group III). Antimicrobial susceptibility testing indicated that all isolates were susceptible to tetracycline, gentamicin, erythromycin, and chloramphenicol, while resistant to ampicillin, cefepime, oxacillin, and rifampin. The analysis of ability of biofilm formation on stainless steel tube showed optical density (OD) value of 66.7% of isolates was greater than 1. The OD level of isolates belonging to group III was higher compared with the other two groups, and OD values of HB1 and HN5 were greater than 2. These findings improved the understanding of the characteristics of isolated from powdered food products in China, and provided a theoretical basis for the prevention and control of in food industry.