The reported inverse correlation between the transcription of tcdC and the toxin genes and the expression patterns of the corresponding proteins, together with the biochemical data, has led to the prevailing model that TcdC is an important repressor of toxin expression [12, 16, 17, 20] . This model seems to be supported by the finding that the absence of a functional TcdC caused by a frame shift mutation (D117 bp) in the tcdC gene is linked to a supposed increased toxin production in certain (hyper) virulent strains [15, 22] .