The exponential growth phase of C. difficile has been reported to be associated with a high transcription level of the tcdC gene and low transcription levels of tcdR and the toxin genes, whereas the stationary growth phase is associated with a low transcription level of the tcdC gene and high transcription levels of tcdR and the toxin genes in strain VPI10463 [16] . The synthesis and secretion of the toxins is increased upon entry into the stationary growth phase [16] [17] [18] [19] . The decreasing transcription of tcdC correlates with diminishing TcdC protein levels in stationary growth phase [16, 20] .