The conversion of aflatoxin B1 by six kinds of fungi, previously reported to assimilate aflatoxin B1, was investigated. The tested fungi were Aspergillus fumigatus, Paecilomyces lilacinus, P. inflatus, Humicola fuscoatra, Penicillium spinulosum, and Trichoderma aureoviride. After incubation at 25°C for 4 weeks, most of the tested fungi lowered the aflatoxin B1 level in the broth to less than 10% of the starting level. Penicillium spinulosum contained 80% of aflatoxin B1 in the mycelia, but the other fungi contained less than 30% of aflatoxin B1 in the mycelia. This fact suggests that aflatoxin B1 was converted by these 5 kinds of fungi. Only Humicola fuscoatra showed a marked difference in the aflatoxin conversion rate between intact and sterilized mycelia. Intact mycelia of the fungus degraded 90% of aflatoxin B1 but sterilized mycelia had no effect on aflatoxin B1. Aflatoxin B1 was converted in the mycelia of the fungus but not in the broth filtrate. These findings indicate that the conversion by Humicola fuscoatra was a biological reaction. The conversion products of aflatoxin B1 by Humicola fuscoatra were identified to be aflatoxicols A and B by TLC and HPLC, and all the reduced aflatoxin B1 was converted to aflatoxicols A and B.
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.
A Survey for contamination of Salmonella from poultry farms in Shimane Prefecture was carried out during the period from April, 1993 to March, 1994. Salmonella were isolated from feces of laying hens and feed in 1 (7.7%) of 13 poultry farms and the detected serotype was only Salmonella Tenessee. The cause of contamination was bonito powder in feed. Salmonella had been isolated for 8 weeks after disinfection in a poultry farm contaminated by Salmonella, but no Salmonella were isolated there after.