Purpose: Bacillus cereus food poisoning is typically associated with toxins. The diversity of Bacillus cereus strains with different toxins is reflected in their broad range of pathogenicity. We conducted a preliminary risk assessment of the Bacillus cereus isolated from Taiwan foodborne illness outbreaks and food survey by characterizing their toxin-producing genes and toxin profiles.
Methods: Bacillus cereus were isolated from outbreak-associated food samples and food survey samples by culture methods and identified with biochemical reactions. The toxin-producing genes for diarrheal enterotoxins (hemolysin BL, non-hemolytic enterotoxin, enterotoxin FM, enterotoxin T, and cell toxin K), and emetic toxin (cereulide) were detected by PCR methods coupled with specific primers for each toxin gene. Immunoassay test kits were used to determine diarrheal toxins, including non-hemolytic enterotoxin and hemolysin BL. Since there was no commercial kit for emetic toxin, a LC-MS method was implemented.
Results: The frequency of Bacillus cereus detected from outbreak-associated samples was around 9%. Among the 189 isolates examined, almost all of them contain one or more toxin-producing genes, but we could not find any isolate that produced emetic toxins. The prevalence of Bacillus cereus in food survey samples was around 16%, and most (98%) were contaminated at a level < 100 CFU/g. However, there were 3 (1.6%) isolates that produced emetic-toxin among the 123 isolates examined.
Significance: Toxin-producing strains of Bacillus cereus show distinct characteristics between different strains. Total counts of Bacillus cereus in food survey samples were low, but the emetic-toxin-producing strains could pose potential risk.