High prevalence of toxin a-negative, toxin b-positive clostridium difficile in Dublin, Ireland

Clostridium difficile is a major cause of infectious diarrhoea in hospitalised patients. Most pathogenic C. difficile strains produce two toxins A and B, however clinically relevant toxin-A-negative-toxin-B-positive (A-B+) strains of C. difficile that cause diarrhoea and colitis have been isolated worldwide. The geographical distribution and significance of these strains in Irish hospitals is unknown. The aim of this study was to determine the prevalence of A-B+ strains in 12 health-care facilities in Dublin, Ireland. Following culture, 123 C. difficile isolates were examined using toxin immunoassays, cytotoxicity assays and PCR. 52 isolates were not detected with the toxin-A ELISA and demonstrated variant cytopathic effects with the cytotoxicty assay. PCR-RFLP revealed that these 52 strains had a 1.8-kb deletion in the tcdA gene and restriction enzyme analysis revealed the loss of polymorphic restriction sites. These 52 A-B+ isolates were designated toxinotype VIII (C. difficile strain-1470). The overall prevalence of A-B+ isolates was 42%, with institutional prevalence rates varying from 0–61%. The prevalence of A-B+ C. difficile in Dublin, Ireland is higher compared with reported prevalence in other countries. This report expands our understanding of this pathogen, identifying a geographical cluster of toxin-variant C. difficile strains in a major Irish population centre.