Correlation between oral toxicity and in vitro stability of Clostridium botulinum type A and B toxins of different molecular sizes

The in vitro sensitivity to acid and pepsin differed markedly among Clostridium botulinum type A and B toxins of different molecular sizes. The larger the molecular size of the toxin, the higher the resistance to these agents. Tye B derivative toxin was rapidly inactivated, but the progenitor toxins resisted in vitro exposure to rat intestinal juice. The molecular dissociation of the progenitor toxins did not occur in rat intestinal juice of pH 7.0, but did occur in a buffer solution of the same pH. The oral toxicity may depend mostly on the stability of toxin molecules in the stomach and, to a less extent, in the intestine. The present results seem to justify the conclusion that C. botulinum type A and B progenitor toxins with molecular sizes larger than 16S are more potent oral toxins than 12S progenitor toxins.