FIG. 4.

Cytotoxicity of 48-h C. difficile cultures on monolayer Vero cells. Isolates of various tcdC types: wt (no deletion), 18-bp deletion associated with a 1-bp deletion at position 117 (characteristic of the PCR ribotype 027 clone), 36-bp, 39-bp, and 54-bp deletions were tested by a cytotoxicity assay. The high-level-toxin-producing reference strain VPI 10463 (wt tcdC gene) was included. The cytotoxicity titer corresponds to the greater dilution giving a morphological alteration in 50% of the cells. Values are averages of duplicate cultures, and bars indicate standard errors.