[Identification of strain B 657 of Clostridium botulinum]

Strain 657 has been described as a toxin variant of Clostridium botulinum type B. Toxin neutralization tests performed with types B and A botulinum antitoxins of known potency, avidity and specificity at 20, 200, 2.000 and 20.000 DL50/mouse level of testing have shown that 657 toxin is a mixture of B (90 to 99% of the complex) and A antigenic fractions. The possibility of a cross contamination between A and B serotypes has been, in principle, ruled out through the serologic screening of 33 toxin samples coming one each from 33 well isolated colonies taken from two colony variants of this strain. Strain 657 produces a new complex toxin and is proposed as the candidate for the prototype of a new C. botulinum serotype: subtype Ba.