Why is Bacillus cereus group enriched in sufu? -A study on prevalence, characterization and traceability

This study aims to investigate the characteristics and contamination sources of the Bacillus cereus group in sufu to enhance food safety control. A total of 90 commercial sufu samples were analyzed, revealing a high contamination rate of 97.8 %, with 6.7 % exceeding the safety limit of 5 log CFU/g. 43 representative isolates from white, red, and spicy sufu varieties were further characterized using PCR-based virulence gene profiling, MLST, and panC gene sequence analysis. Virulence gene profiling revealed universal presence of nheABC and entFM (100 %), with cytK and the complete hblACD cluster present in 44.8 % and 11.6 % of isolates, respectively. Isolates harboring the complete nheABC or hblACD genes were confirmed to produce the corresponding Nhe or Hbl enterotoxins in soymilk. MLST and panC sequencing revealed distinct phylogenetic profiles among the isolates, with heat-resistant strains being frequently identified. To trace contamination routes, samples from a production facility, including environmental surfaces, equipment, raw materials, and semi-finished products, were analyzed using microbial culture and RAPD. The solid-state fermentation stage was identified as the critical control point for B. cereus proliferation, with raw soybeans and air serving as primary reservoirs. B. cereus introduced via raw materials adhered to equipment, forming persistent biofilms that facilitated cross-contamination. Conventional cleaning and disinfection procedures (on-site cleaning, standard food disinfectants) demonstrated limited efficacy against these biofilms. These findings systematically clarify the hazard characteristics, genetic background, and contamination pathways of B. cereus in sufu production, providing a scientific basis for targeted intervention and sanitation optimization in industrial processing.