Purpose: The objective of this study was to assess the prevalence, toxin profiles, and phenotype of B. cereus from RTE vegetables.
Methods: A total of 155 individually packed RTE vegetables were purchased from retail stores in South Korea. The confirmation of possession of diarrheal and emetic toxin genes such as nheABC, hblCDA, cytK, entFM, EM1, and ces was performed by using PCR assay. Biochemical tests including starch fermentation, salicin hydrolysis, hemolysis, motility tests, and lecithinase were conducted for all isolates. To assess B. cereus psychrotrophic growth characteristics, all strains were inoculated onto sheep blood agar, and plates were incubated at 7°C over a period of 21 days.
Results: We found that 70 of the 155 (45%) tested retail vegetable salad and sprout samples were positive for B. cereus. The B. cereus isolates harbored at least one enterotoxin gene. The detection rates of nheABC, hblCDA, cytK, and entFM enterotoxin genes among all isolates were 97.1%, 100%, 81.4%, and 98.6%, respectively. No strain carried the emetic toxin genes such as EM1 and ces. The percentage of strains that were positive for salicin hydrolysis, starch fermentation, hemolysis, motility test, and lecithinase hydrolysis were 91.4%, 95.7%, 80%, 100%, and 100%, respectively. Only six strains (8.6%) from the 70 isolates were psychrotrophic and were able to grow at 7°C. All of the psychrotrophic isolates possessed at least 1 enterotoxin gene.
Significance: Considering the high contamination levels and the toxin profiles of B. cereus in RTE vegetables, the products should be evaluated by using strict microbial safety standards and post-processing control measures that ensure product safety.