Genomic relatedness of Clostridium difficile strains from different toxinotypes and serogroups

Clostridium difficile strains can be divided into sixteen toxinotypes (0 and I to XV) according to changes in their toxin genes. To determine the genomic similarity between toxinotypes, two molecular typing techniques were used, 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), and strains with variant toxin genes from toxinotypes III, TV, V, VI, VII, VIII, IX, and XI. The strains studied formed three main clusters, which correlated well with serogroups: in the first were strains from serogroup A15 and E; in the second, serogroup Al strains; and in the third, strains from serogroups F and X. Within these three clusters strains of a single toxinotype were grouped together. Toxinotypes III, IV and VIII were more similar to strains with ordinary toxin genes or non-toxinogenic isolates within the same serogroup than to other toxinotypes. Toxinotypes V, VI, VII, and XI, which exhibit similar changes in their toxin genes, seem to be more closely related one to another than to other toxinotypes. It can be concluded that variant Clostridium difficile strains do not have a common ancestor and that groups of different toxinotypes arose independently from strains with ordinary toxin genes. (C) 2000 Academic Press.