Poster Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

Identification and analysis of virulence factors in Clostridium difficile (#150)

Briony Elliott 1 , Thomas V. Riley 1 2
  1. Microbiology and Immunology, School of Pathology and Laboratory Medicine, University of Western Australia, Crawley, WA, Australia
  2. Department of Microbiology, PathWest Laboratory Medicine, QE2 Medical Centre, Nedlands, WA, Australia

The gram-positive, spore-forming bacterium Clostridium difficile is an important nosocomial pathogen and the most frequent cause of infectious hospital-acquired diarrhoea. The two main virulence factors of C. difficile are toxin A and toxin B, the genes for which are both situated on a 19.6-kb genetic element, known as the PaLoc. Some strains also produce an ADP-ribosyltransferase known as binary toxin. Despite the large accessory genome (~80%), and the high prevalence of mobile elements (~10%) in the C. difficile genome, relatively little work has been done on additional virulence factors. In this study, we used genomic data to identify potential virulence factors in C. difficile. More than 50 individual genes or gene clusters were identified, 18 of which were selected for PCR screening. A selection of 236 C. difficile strains was assembled to represent a diverse group of isolates, including both toxigenic and non-toxigenic strains, known hypervirulent strains, and strains from diverse sources (animal, human and environment). The overall frequency of the target genes ranged from 12.1% to 99.2%. Several significant differences in virulence gene profiles were observed. The presence of the PaLoc was significantly associated with the presence of genes encoding proteins involved in capsule synthesis (CD2769), adhesion (CD2831, CD2592), motility (CD3294), or the degradation of extracellular matrix components (NT03CD0500, CD2797, CD2787). In strains with increased virulence, significant differences were seen with ribotypes 015 and 018, but not with 027 where disease severity has been largely linked to a variant toxin B. Adhesion genes were more frequent in the common non-toxigenic ribotype 010 strain compared to other non-toxigenic strains, explaining at least in part the success of this “commensal” strain in the community.
This study highlights the potential role of accessory virulence factors in C. difficile which need to be studied further.