BACKGROUND: Clostridium sordellii can cause severe infections in animals and humans, the latter associated with trauma, toxic shock and often-fatal gynaecological infections. Strains can produce two large clostridial cytotoxins (LCCs), TcsL and TcsH, related to those produced by Clostridium difficile, Clostridium novyi and Clostridium perfringens, but the genetic basis of toxin production remains uncharacterised. RESULTS: Phylogenetic analysis of the genome sequences of 44 strains isolated from human and animal infections in the UK, US and Australia placed the species into four clades. Although all strains originated from animal or clinical disease, only 5 strains contained LCC genes: 4 strains contain tcsL alone and one strain contains tcsL and tcsH. Four toxin-positive strains were found within one clade. Where present, tcsL and tcsH were localised in a pathogenicity locus, similar to but distinct from that present in C. difficile. In contrast to C. difficile, where the LCCs are chromosomally localised, the C. sordellii tcsL and tcsH genes are localised on plasmids. Our data suggest gain and loss of entire toxigenic plasmids in addition to horizontal transfer of the pathogenicity locus. A high quality, annotated sequence of ATCC9714 reveals many putative virulence factors including neuraminidase, phospholipase C and the cholesterol-dependent cytolysin sordellilysin that are highly conserved between all strains studied. CONCLUSIONS: Genome analysis of C. sordellii reveals that the LCCs, the major virulence factors, are localised on plasmids. Many strains do not contain the LCC genes; it is probable that in several of these cases the plasmid has been lost upon laboratory subculture. Our data are consistent with LCCs being the primary virulence factors in the majority of infections, but LCC-negative strains may precipitate certain categories of infection. A high quality genome sequence reveals putative virulence factors whose role in virulence can be investigated.

Clostridium difficile is a major cause of infectious diarrhea in hospitalized patients. Clostridium difficile-associated disease (CDAD) is of gaining importance now due to its increasing incidence and severity. However, little is known about the C. difficile infections in the Czech Republic. The aim of the study was to characterize C. difficile strains recently isolated (2008 to 2011) from patients hospitalized with gastrointestinal disease in four Prague health care institutions using molecular typing methods; PCR toxinotyping, PCR ribotyping and MLVA (multilocus variable number tandem repeat analysis). Among 273 C. difficile strains, we identified 8 toxinotypes (0, III, IV, V, VI, VIII, IX a XXIII) and 63 ribotypes, of which ribotypes 596 (23,4 % patient), 017 (13,9 %) and 176 (7 %) were the most frequent. According to PCR ribotyping, the situation in the Czech Republic is the most similar to the situation in Poland. Within ribotypes 017, 017/1 and 017/2 and ribotypes 596 and 596/1, 5 and 4 distinct clusters were identified by MLVA, none of which was institution-specific. Additionally, pathogenic C.difficile were isolated from piglet faeces (63,3 %) in a single piglet farm, evaluating the role of C. difficile as an emerging animal pathogen. All piglet isolates belonged to the toxinotype 0 and the ribotype...