Fig. 1

Phylogenetic tree of the slpA protein from 26 strains/16 major ribotypes of C. difficile. Each leaf on the tree refers to a specific ribotype, these are named by ribotype number as per convention. The branch numbering scheme is shown in grey. Ribotypes with very short branch lengths are given as clusters at the tips of branches. All but three nodes had posterior probability value (PP) = 1.00: two of these values are shown in italics on the tree (0.99 and 0.89). The final exception was the node joining ribotypes 046 and 092, where * denotes PP of 0.82. Lineages under positive selection are highlighted as follows; blue corresponds to positively selected sites detected in the HMW protein, and red corresponds to positively selected sites in the LMW protein. Where known, the virulence/severity of disease associated with each ribotype is denoted by a red “+” for hypervirulence