Oral toxicities of Clostridium botulinum type A and B toxins from different strains

The production and the oral toxicity for mice of Clostridium botulinum type A and B toxins of different strains were studied. All five type B strains produced both 16S (large or L) and 12S (medium or M) toxins, although the relative amounts varied with the strains. The culture supernatant of type B Okra strain was the most potent in oral toxicity. The L toxin of this culture was about 700 times more toxic in feeding tests with mice than the L toxin from type B strain NH-2, whereas the M toxins of the two strains had the same oral toxicity. These results indicate that the oral toxicity of type B toxin varies with the culture strain. Oral toxicities of L toxin produced by type A strains 62A and 97 were comparable but were 10 times higher than those of their M toxins. Hybrids of toxic and nontoxic components separated from L toxins of type B strains Okra and NH-2 revealed that the high oral toxicity of the B-L toxin of strain Okra is attributable not to the toxic but to the nontoxic component of the toxin. The present study suggests that the 16S molecular-sized toxin elaborated by a certain strain of C. botulinum type B is implicated in the high fatality rate in type B human botulism.