FURTHER EVIDENCE FOR THE GENETIC-HETEROGENEITY OF CLOSTRIDIUM-BOTULINUM AS DETERMINED BY 23S RDNA OLIGONUCLEOTIDE PROBING

A stretch of the 23S rDNA from Clostridium botulinum strains that prod uce different types of neurotoxins was sequenced and three rDNA oligon ucleotide probes designed. They were labelled non-radioactively with D IG-ddUTP and tested for specificity by dot blot hybridization against rRNA of 83 strains of clostridia and other Gram-positive organisms. Th e probes discriminated between groups of C. botulinum strains defined by their toxin types thus supporting previous results on DNA-DNA and D NA-rRNA similarity studies and phenotypic characterization: (i) proteo lytic C. botulinum strains with toxins of types A, B and F, as well as the closely related strains of C. sporogenes and C. putrificum and a strain of C. barati that produces a botulinum toxin of type F; (ii) no n-proteolytic C. botulinum strains with toxins B and E; (ii) C. botuli num with toxin type D, and (iii) C. argentinense (formerly C. botulinu m) with botulinum toxin type G, as well as C. subterminale. These prob es extend the spectrum of C. botulinum probes published recently for n on-proteolytic C. botulinum types B, E and F (Campbell et al., 1993).