Genomic relatedness of Clostridium difficile strains from different toxinotypes and serogroups

Clostridium difficile strains can be divided into sixteen toxinotypes (0 an d I to XV) according to changes in their toxin genes. To determine the geno mic similarity between toxinotypes, two molecular typing techniques were us ed, AP-PCR and PFGE. Strains were selected from five serogroups (Al, A15, E , F, X) and represented non-toxinogenic isolates, strains with toxin genes identical to the reference C. difficile strain, VPI 10463 (toxinotype 0), a nd strains with variant toxin genes from toxinotypes III, TV, V, VI, VII, V III, IX, and XI. The strains studied formed three main clusters, which corr elated well with serogroups: in the first were strains from serogroup A15 a nd E; in the second, serogroup Al strains; and in the third, strains from s erogroups F and X. Within these three clusters strains of a single toxinoty pe were grouped together. Toxinotypes III, IV and VIII were more similar to strains with ordinary toxin genes or non-toxinogenic isolates within the s ame serogroup than to other toxinotypes. Toxinotypes V, VI, VII, and XI, wh ich exhibit similar changes in their toxin genes, seem to be more closely r elated one to another than to other toxinotypes. It can be concluded that v ariant Clostridium difficile strains do not have a common ancestor and that groups of different toxinotypes arose independently from strains with ordi nary toxin genes. (C) 2000 Academic Press.