The present invention provides a novel isolated plasmid, wherein the plasmid is a native plasmid found in unique C. botulinum type A strains and encode either BoNT/A3 or BoNT/A4 and BoNT/B. The present invention also provides a method of obtaining a plasmid-encoded botulinum neurotoxin and botulinum neurotoxin complex comprising the step of isolating a plasmid encoding the cntA/A or cntA/B neurotoxin gene and genes encoding protein components of the toxin complex from a C. botulinum type A strain. The inventors performed comparative analyses of representative BoNT/A subtype strains by pulsed-field gel electrophoresis (PFGE) and Southern hybridizations with probes specific for the BoNT/A and B genes, cntA/A and cntA/B. Unexpectedly, the inventors determined that the genes encoding BoNT/A3 in the A3 strain, and BoNT/A4 and BoNT/B in the A4 strain, are on plasmids.
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