The relative role of toxins a and b in the virulence of clotridioides difficile

Andrew M. Skinner, S. Tyler Phillips, Michelle M. Merrigan, Kevin J. O’leary, Susan P. Sambol, Farida Siddiqui, Lance R. Peterson, Dale N. Gerding, Stuart Johnson*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Most pathogenic strains of C. difficile possess two large molecular weight single unit toxins with four similar functional domains. The toxins disrupt the actin cytoskeleton of intestinal epithelial cells leading to loss of tight junctions, which ultimately manifests as diarrhea in the host. While initial studies of purified toxins in animal models pointed to toxin A (TcdA) as the main virulence factor, animal studies using isogenic mutants demonstrated that toxin B (TcdB) alone was sufficient to cause disease. In addition, the natural occurrence of TcdA−/TcdB+ (TcdA−/B+)mutant strains was shown to be responsible for cases of C. difficile infection (CDI) with symptoms identical to CDI caused by fully toxigenic (A+/B+) strains. Identification of these cases was delayed during the period when clinical laboratories were using immunoassays that only detected TcdA (toxA EIA). Our hospital laboratory at the time performed culture as well as toxA EIA on patient stool samples. A total of 1.6% (23/1436) of all clinical isolates recovered over a 2.5-year period were TcdA−/B+ variants, the majority of which belonged to the restriction endonuclease analysis (REA) group CF and toxinotype VIII. Despite reports of serious disease due to TcdA−/B+ CF strains, these infections were typically mild, often not requiring specific treatment. While TcdB alone may be sufficient to cause disease, clinical evidence suggests that both toxins have a role in disease.

Original languageEnglish (US)
Article number96
Pages (from-to)1-9
Number of pages9
JournalJournal of Clinical Medicine
Issue number1
StatePublished - Jan 2021


  • Clostridioides difficile
  • Molecular epidemiology
  • Restriction endonuclease analysis
  • Toxin A
  • Toxin B
  • Toxinotyping

ASJC Scopus subject areas

  • General Medicine


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