Emergence of a ribotype 244 strain of Clostridium difficile associated with severe disease and related to the epidemic ribotype 027 strain

Abstract

Background: We identified 12 patients with Clostridium difficile infection between July 2011 and March 2012 from whom an unusual C. difficile strain was isolated. This strain had a single-nucleotide deletion of the tcdC gene at position 117 and binary toxin genes, which are characteristic of the hypervirulent ribotype (RT) 027 strain.

Methods: A retrospective cohort study of 12 patients infected with C. difficile RT244 and 24 patients infected with non-RT244/non-RT027 strains matched for place of diagnosis and time of collection of specimen was performed. We performed whole-genome sequencing to understand the relationship of the RT244 strain to other C. difficile strains and further understand its virulence potential.

Results: Clostridium difficile RT244 was associated with more severe disease and a higher mortality rate. Phylogenomic analysis using core genome single-nucleotide polymorphisms showed that RT244 is in the same genetic clade (clade 2) as RT027 but is distinct from all RT027 strains. The pathogenicity locus of the RT244 strain encodes a variant toxin B, and this was confirmed by demonstration of Clostridium sordellii-like cytopathic effect on Vero cells. Toxin B production in culture supernatants was lower than that seen with a RT027 strain.

Conclusions: Our findings demonstrate the pathogenic potential of this RT244 C. difficile strain and emphasize the importance of ongoing surveillance for emergent strains.

Keywords: Clostridium difficile; toxin B; virulence; whole-genome sequencing.