Antibiotic-resistant toxin A-negative toxin B-positive Clostridium difficile in Dublin, Ireland

Abstract number: 1133_11

Drudy D., Harnedy N., Fanning S., O'Mahony R., Kyne L.

C. difficile is a major cause of infectious diarrhoea in hospitalised patients. Clinically important toxin A-negative, toxin B-positive strains of C. difficile that cause diarrhoea and pseudomembranous colitis in humans have recently been isolated worldwide. The aims of this study were to investigate a C. difficile outbreak in one university-affiliated hospital in Dublin, Ireland and to determine the prevalence of toxin A-negative, toxin B-positive C. difficile in other care institutions in the greater Dublin area. For the outbreak investigation, we prospectively studied all consecutive patients with nosocomial C. difficile diarrhoea between August 2003 and January 2004. . For the prevalence study, toxin positive faecal samples (n = 123) were collected between February and August 2004 from a twelve different institutions in Dublin Ireland. C. difficile was cultured from faecal specimens. Toxin-specific enzyme immunoassays, IMR-90 cytotoxicity assay and PCR were used to analyse C. difficile isolates. Antibiotic sensitivities were determined using E-tests. Seventy-three cases of C. difficile diarrhoea were identified during the outbreak study period. Studies examining in vitro production of toxin A and B showed that ninety-five % of isolates tested negative for production of toxin A but were positive when investigated using the cell culture cytotoxicity assay. These toxin A-negative, toxin B-positive C. difficile isolates had a 1.7 kb deletion in the tcdA gene. PCR ribotyping determined that these isolates were clonal. The clonal outbreak isolates were resistant to all fluoroquinolones (MIC's of >32 mg ml^­1) and MLS antibiotics tested (MIC's of >256 mg ml^­1). In the prevalence study, 52 of 123 C. difficile isolates, (42%) were toxin A-negative, toxin B-positive. Prevalence rates per institution varied from 0–62%. In the three University teaching hospitals the prevalence rates were 18%, 40%, and 59% respectively. Using PCR, these toxin A-negative, toxin B-positive strains had the same deletion described for the outbreak study (toxinotype VIII strains e.g., C. difficile serotype F, 1470). Toxin A-negative, toxin B-positive C. difficile appears to be prevalent in hospitals in the greater Dublin area and caused at least one hospital outbreak. This report adds to the expanding body of literature reporting the increasing incidence and widespread geographical distribution of clinically important toxin-variant C. difficile strains.