FIG. 6.

qRT-PCR analysis of cprA and cprK expression with the addition of plasmid-encoded cprK. C. difficile wild-type and MC119 strains carrying control vector pMC123 (MC137 and MC164, respectively) or pMC147 (MC162 and MC163) were grown in BHIS medium supplemented with 10 μg/ml thiamphenicol with or without the addition of 10 μg/ml nisin to an OD₆₀₀ of 0.4. RNA was harvested, cDNA synthesized, and qPCR performed using gene-specific primers for cprK (A) or cprA (B). Results were normalized to an internal control gene (rpoC) and graphed as the ratio of each transcript level to that of rpoC and then normalized to the wild type grown without nisin. The means and standard deviations of biological replicates are shown (*, P ≤ 0.05 by Student's t test).