According to the report by HUGHES et. al., a vacuolation activity affecting HEp-2 culture cells was detected in culture filtrate of Bacillus cereus in cooked rice suspension. Fourty-four (78.5%) out of 56 B. cereus strains associated with emetic-syndrome food poisonings and three out of 16 strains from commercial foods produced the vacuolation activity. Fourty-two out of 53 H-1 serotype strains and two H-12 strains were positive in the vacuolation activity. Strains BC1364 and BC1040 isolated from emetic-syndrome food poisoning and strain BC18 isolated from commercial food were tested for the producibility of the activity in various media other than cooked rice suspension, viz., suspensions of cooked spaghetti, tofu, croquette and skim milk, BHIG broth, plain sporulation broth, and that supplemented with each of starch, skim milk, egg york, lecithin and rice oil. In all media except tofu suspension and sporulation broth, strains BC1364 and BC1040 produced the vacuolation activity, but strain BC18 produced no activity in any medium. The vacuolation activity was detected in the culture filtrate after the initiation of spore formation under shaking culture condition at 32°C. The activity was found to be resistant against heating at 100°C for 120 min and 115°C for 60 min, acid, alkaline and proteases.
