Genetic Diversity among Clostridium botulinum Strains Harboring bont/A2 and bont/A3 Genes

Clostridium botulinum type A strains are known to be genetically diverse and widespread throughout the world. Genetic diversity studies have focused mainly on strains harboring one type A botulinum toxin gene,bont/A1 , although all reportedbont/A gene variants have been associated with botulism cases. Our study provides insight into the genetic diversity ofC. botulinum type A strains, which containbont/A2 (n = 42) andbont/A3 (n = 4) genes, isolated from diverse samples and geographic origins. Genetic diversity was assessed by usingbont nucleotide sequencing, content analysis of thebont gene clusters, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE). Sequences ofbont genes obtained in this study showed 99.9 to 100% identity with otherbont/A2 orbont/A3 gene sequences available in public databases. The neurotoxin gene clusters of the subtype A2 and A3 strains analyzed in this study were similar in gene content.C. botulinum strains harboringbont/A2 andbont/A3 genes were divided into six and two MLST profiles, respectively. Four groups of strains shared a similarity of at least 95% by PFGE; the largest group included 21 out of 46 strains. The strains analyzed in this study showed relatively limited genetic diversity using either MLST or PFGE.