Type A and B neurotoxin genes in a Clostridium botulinum type AB strain

The genetic structure of neurotoxin genes in a Clostridium botulinum strain producing both type A and B neurotoxins (type AB) was investigated. Analyses by polymerase chain reaction (PCR) using type-specific primers corresponding to the coding regions for N-terminals of light-chains and C-terminals of heavy-chains of type A and type B neurotoxins, and Southern hybridization of total DNA showed that the type AB strain I.P.7212 carries at least one copy each of type A and B neurotoxin genes. Partial nucleotide sequences obtained by direct sequencing of the PCR products indicate that the type A and B genes carried by this strain are not classical type A and non-proteolytic type B genes, but are similar to the type A gene present in a strain which had caused infant botulism in Kyoto and the type B gene present in a proteolytic type B strain.