Genotyping, Antimicrobial Susceptibility and Biofilm Formation ofBacillus cereusIsolated from Powdered Food Products in China

This study was conducted to reveal the genotyping, antimicrobial susceptibility, and biofilm formation ofBacillus cereusisolated 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-twoB. cereusstrains were detected with an overall contamination rate of 8.4%, as well as, the highestB. cereuscontamination 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 ofB. cereuswere 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)(595)value of 66.7% ofB. cereusisolates was greater than 1. The OD(595)level of isolates belonging to group III was higher compared with the other two groups, and OD(595)values ofB. cereusHB1 and HN5 were greater than 2. These findings improved the understanding of the characteristics ofB. cereusisolated from powdered food products in China, and provided a theoretical basis for the prevention and control ofB. cereusin food industry.

Automated summary

This study in China revealed the genotyping, antimicrobial susceptibility, and biofilm formation of Bacillus cereus isolated from powdered food products. The findings showed the distribution and characteristics of this bacterium in different provinces and types of food products.