Type IV pili (T4P) are the only type of bacterial pili known to be produced by both Gram-negative
and Gram-positive organisms. Though the main pilus shaft consists primarily of only one protein (the major pilin), T4P are unusual in their complexity, requiring multiple (10 or more) different protein components for assembly. Like most types of pili, T4P often function as virulence factors. In particular, T4P frequently operate as adhesins, enabling bacteria on which they are present to stick to each other (to form a biofilm or suchlike) or to adhere directly to host cells. Many T4P systems are able to retract, in which case the T4P may mediate flagella-independent motility. Most research into T4P has historically been performed on Gram-negative organisms,
with T4P-encoding genes only being identified in Gram-positive organisms more recently. In
particular, all sequenced species of the genus Clostridium are known to encode T4P, but only
minimal investigation of these systems has been performed to date. In this study, the T4P of
Clostridium difficile were investigated. C. difficile is an important pathogen, being the leading
cause of antibiotic-associated diarrhoea in the developed world and thus a considerable burden
on Western healthcare systems. By investigating the T4P of this species it was hoped to further
elucidate its mechanisms of pathogenicity. Data is presented demonstrating the control of T4P
expression by cyclic-di-GMP, and identifying which genes are essential for T4P production in
C. difficile. Additionally, a genomic analysis of the related pathogen Clostridium sordellii was
performed, using the first high quality genome sequence produced for this species. Genes
encoding T4P were identified, analysed and investigated. Furthermore, plasmids carrying the
genes encoding the species’ key virulence factors (Lethal Toxin, TcsL, and in some cases haemorrhagic toxin, TcsH) were identified. These plasmids appear to be unstable, a fact with
significant implications for diagnosis of C. sordellii disease.