Clostiridum difficile and Clostridium sordellii are two members of the Clostridia that cause toxin-mediated diseases in humans and animals. C. difficile is a leading cause of antibiotic associated nosocomial diarrhoea. The major virulence factors contributing to the pathogenesis of C. difficile infections are toxins A and B. These two large clostridial toxins are exotoxins, however they do not encode typical N-terminal signal peptides. For this reason, the export mechanism of these toxins is unknown. The tcdA and tcdB genes, encoding toxins A and B, respectively, are located in the pathogenicity locus of C.difficile and flank the tcdE gene. TcdE is predicted to be structurally similar to bacteriophage holin proteins, which are involved in the lysis of host bacterial cells, facilitating the release of progeny phage. C. sordellii, which is similar to C. difficile, causes disease in humans and animals. In humans, diseases include toxic shock syndrome, myonecrosis and sepsis. These infections are usually fatal and often occur after trauma, pregnancy and injection drug use. The major virulence factor associated with C. sordellii disease is the exotoxin TcsL, another large clostridial toxin. In this study, bioinformatic analysis revealed the presence of a tcdE gene orthologue in C. sordellii, designated tcsE. Results from in vitro cell cytoxicity assays using supernatants derived from tcdE or tcsE mutant strains were found to be significantly less toxic compared to their respective wild type strain. In addition, in an in vivo murine C.difficile infection model, tcdE mutant strains were attenuated in virulence in comparison to the wild type strain, suggesting that TcdE might be an important factor contributing to C. difficile virulence. These results suggest that proteins encoded by the holin-like genes, tcdE and tcsE, may be involved in the export of the large clostridial toxins of C. difficile and C. sordellii, respectively.