Clostridium botulinum subtype Ba.

Strain 657 has been described as a toxin variant of Clostridium botulinum type B. Neutralization tests performed with types A and B botulinal antitoxins of known potency and avidity at 20, 25, 50, 100, 200, 2,000 and 20,000 mouse LD50 levels of testing, have shown that 657 toxin is a mixture of B (approximately 95% of the complex) and A antigenic fractions. The possibility of a cross-contamination between A and B serotypes has been practically ruled out through the serologic screening of the toxins from 100 well isolated colonies taken from two colony variants of this strain. Strain 657 rabbit antitoxin possesses A and B neutralizing activities. Strain B 657 produces a hitherto undescribed complex toxin and it represents the prototype of a new C. botulinum serotype, subtype Ba.