An independent study, published during the preparation of this manuscript, reached a similar conclusion with respect to the role of TcdC in toxin regulation in C. difficile 630Derm using an allelic exchange technique [38] . In that paper reintroduction of a single functional copy of tcdC at its native locus did not affect toxin production in strain R20291 either [38] . R20291 is a strain from problematic PCR ribotype 027 (NAP1/REA B1) that was isolated following an outbreak in Stoke Mandeville, UK.