Characterization of Bacillus cereus isolates from raw soybean sprouts

Raw soybean sprouts, which are used as ingredients in cook-chilled products, were analyzed to evaluate the incidence of mesophilic aerobic microorganisms, psychrotrophic microorganisms, anaerobic microorganisms, coliforms, and spore-forming microorganisms Bacillus cereus, Clostridium botulinum, and Clostridium perfringens. Mesophilic microorganisms on raw soybean sprouts were present in large populations, 5.5 x 10(6) to 1.4 x 10(8) CFU/g, and psychrotrophic microorganisms were found to be more numerous than the other groups. Coliforms accounted for 15% of mesophilic microorganism counts on average, and the average for spore-forming microorganisms was 5.2 x 10(2) CFU/g. B. cereus was isolated from 12 of 17 soybean sprout samples, whereas C. botulinum and C. perfringens were not isolated. B. cereus was isolated in greater numbers at 30 degrees C compared with other temperatures and was not isolated at 4 degrees C. Of the 55 strains isolated from soybean sprouts, 52 were positive for starch hydrolysis, and only 3 strains did not hydrolyze starch. Among the 55 strains of B. cereus isolates, 53 showed the ability to produce diarrheal enterotoxin by CRET-RPLA.