Fig 1.

Dose-response curves of in vitro toxin-induced caspase activity: C. difficile TcdA on Vero cells (A), C. difficile TcdB on Vero cells (B), C. difficile binary toxin CDTa-CDTb on Vero cells (C), C. diphtheriae toxin on HeLa cells (D), and P. aeruginosa exotoxin A on HeLa cells (E). Caspase induction was measured in toxin-treated cell cultures using the Caspase-Glo 3/7 assay kit (Promega), and the results are shown as mean luminescence (measured in relative light units [RLU]) ± the standard deviation for 5 replicate wells across 2 assays. The EC₅₀ (50% effective concentration) was calculated by four-parameter logistic regression fitting of the titration curve.