TcdR is an alternative sigma factor that positively regulates toxin production [11, 12] . The direct interaction of TcdR and the RNA polymerase core enzyme mediates recognition of the toxin promoters and the tcdR promoter [11, 12, 21] . TcdC has been reported to act like an anti-sigma factor for toxin production by destabilizing the TcdR-RNA polymerase core enzyme complex in a way that is not yet fully understood [12] .