Fig. 7
Normalized in vitro Toxin A and B production differs between non-epidemic and epidemic ribotype isolates at 72-h. The 13 isolates (7 non-epidemic and 6 epidemic) were cultured in SM broth over a 72-h period. a Toxin A and b Toxin B production was determined from spent medium by ELISA and normalized per 106 vegetative cells recovered. c Toxin A and d levels at 72 h in culture for each of the individual isolates are shown. Mean toxin titers for non-epidemic isolates are represented by the black bars, and mean toxin titers for epidemic isolates are represented by the gray bars. These data represent the average of three independent experiments, and error bars indicate the standard errors of the means. An asterisk denotes significant difference at p < 0.05 (Two-way ANOVA with Tukey’s post-hoc test; p < 0.05)