Atypical toxin variant of Clostridium botulinum type B associated with infant botulism

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Abstract
An atypical toxin variant of C. botulinum (strain 657) was isolated from the feces of a 6 wk old female infant whose symptoms and clinical history were consistent with infant botulism. Toxin detected in the feces and the toxin produced by isolates from the feces and from 2 rectal swabs could be neutralized by type B botulinal antitoxin only at very high ratios of antitoxin to toxin in the neutralization mixture. One IU of type B antitoxin neutralized only .apprx. 10 lethal doses of 657 toxin as compared with .apprx. 10,000 lethal doses of conventional type B toxin from the Beans strain. Antitoxin prepared against 657 toxin was 10 times more effective against the conventional toxin than against the homologous toxin. Toxoid-antitoxin-binding studies indicate that both 657 toxin and type B are heterogeneous and that both toxins may contain the same molecular variants, but that the proportions of the variants are different in each.