Abstract
Bacillus thuringiensis was present in 29 out of 137 imported soybean specimens and 10 out of 43 Japanese specimens. The bacterial load was estimated to be less than 102cfu/g. The B. thuringiensis isolates from the imported specimens consisted of 12 serovars; 3a3b3c, 3a3d, 4a4d, 5a5b, 5a5c, 6, 7, 8a8b, 8a8c, 8a8d, 11a11c and 18. The isolates from the Japanese specimens consisted of 6 serovars; 3a3b3c, 4a4d, 5a5b, 6a6c, 8a8c and 22. Serovars 7, 5a5b and 3a3b3c, which are formulated for the BT pesticide, were present in 11, 7 and 6 samples, respectively. Other serovars were detected from a few samples. In addition, B. thuringiensis was detected at around 102cfu/g from 3 out of 30 commercial beancurd specimens, and the isolates were all 3a3b3c.
All B. thuringiensis isolates from soybeans and beancurd were starch hydrolyzers. More than 2μg/ml of diarrheal enterotoxin was produced by one strain of serovar 7, but all other strains produced only small amounts. Also, most strains had no vacuolation activity on HEp-2 cells except a few strains with weak activity.
The beancurd product manufactured from soybeans inoculated with 105cfu/g of serovar 3a3b3c which produced diarrheal enterotoxin, had a bacterial count of 102cfu/g. During storage of the beancurd at 4°C, B. thuringiensis did not grow for 2 days. At 20 or 30°C, the bacterial count increased to 107-108cfu/g after 2 days. More than 2μg/g of the enterotoxin was yielded in the beancurd during storage for 2 days at 30°C, although the enterotoxin was not produced during the storage at 4 or 20°C.
