Fig 4.

Complementation of the tcsR mutant with C. sordellii tcsR (A) or C. difficile tcdR (B). The tcsR or the tcdR genes were cloned under a tetracycline-inducible promoter. The resulting plasmid constructs and the vector alone were introduced into the tcsR mutant for complementation. Bacterial cultures at an OD₆₀₀ of 0.5 were induced for 4 h, and the toxins in the cytoplasm were quantified by ELISA. The signal from the test was recorded as the absorbance at 405 nm. The data shown are means ± standard errors of the means of three replicate samples. Student's t test was used for statistical analysis. **, P ≤ 0.01.