Recently, some doubts were raised about the importance of TcdC for regulation of toxin expression on the basis of two findings. First, two studies have found increasing levels of tcdC transcription in time that coincide with increasing transcription of the toxin genes and increasing amounts of toxin production [18, 19] . Second, there is a great variability in toxin expression levels among (hyper) virulent strains, even though these generally carry mutations in tcdC [15, 18, 19] . Therefore, a minor (or modulatory) role for TcdC in the regulation of toxin expression was proposed [18, 19] .