Isolation and characterisation 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 in humans have been isolated worldwide. The aims of this study were to isolate and characterise A- B+ strains from two university hospitals in Dublin, Ireland. Samples positive for C. difficile were identified daily by review of ELISA results and were cultured on selective media. Following culture, toxin-specific immunoassays, IMR-90 cytotoxicity assays and PCR were used to analyse consecutive C. difficile isolates from 93 patients. Using a toxin A-specific ELISA, 52 samples produced detectable toxin. All isolates were positive using a toxin A/B ELISA. Similarly, all isolates were positive with the cytoxicity assay, although variant cytopathic effects were observed in 41 cases. PCR amplification of the toxin A and toxin B genes revealed that 41 of the previous A- B+ strains had a c. 1.7-kb deletion in the 3'-end of the tcdA gene. Restriction enzyme analysis of these amplicons revealed the loss of polymorphic restriction sites. These 41 A- B+ isolates were designated toxinotype VIII by comparison with C. difficile strain 1470. PCR ribotyping revealed that all A- B+ isolates belonged to PCR-ribotype 017. A- B+ C. difficile isolates accounted for 44% of the isolates examined in this study, and appeared to be isolated more frequently in Dublin, Ireland, than reported rates for other countries.
Drudy
D
D
Centre for Food Safety, School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Dublin, Ireland. denise.drudy@ucd.ie
Harnedy
N
N
Fanning
S
S
O'Mahony
R
R
Kyne
L
L
D001426:Bacterial Proteins / Q000032:analysis* / Q000235:genetics; D001427:Bacterial Toxins / Q000032:analysis* / Q000235:genetics; D016360:Clostridioides difficile / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D004768:Enterotoxins / Q000032:analysis* / Q000235:genetics; D016133:Polymerase Chain Reaction; D021521:Ribotyping
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004768:Enterotoxins; C041348:tcdA protein, Clostridium difficile; C031815:toxB protein, Clostridium difficile