Truncation in the tcdC region of the Clostridium difficile PathLoc of clinical isolates does not predict increased biological activity of Toxin B or Toxin A

BMC Infect Dis. 2009 Jun 28;9:103. doi: 10.1186/1471-2334-9-103.


Background: The increased severity of disease associated with the NAP1 strain of Clostridium difficile has been attributed to mutations to the tcdC gene which codes for a negative regulator of toxin production. To assess the role of hyper-production of Toxins A and B in clinical isolates of Clostridium difficile, two NAP1-related and five NAP1 non-related strains were compared.

Methods: Sequencing was performed on tcdC, tcdR, and tcdE to determine if there were differences that might account for hyper-production of Toxin A and Toxin B in NAP1-related strains. Biological activity of Toxin B was evaluated using the HFF cell CPE assay and Toxin A biological activity was assessed using the Caco-2 Trans-membrane resistance assay.

Results: Our results confirm that Toxin A and Toxin B production in NAP1-related strains and ATCC 43255 occurs earlier in the exponential growth phase compared to most NAP1-nonrelated clinical isolates. Despite the hyper-production observed in ATCC 43255 it had no mutations in tcdC, tcdR or tcdE. Analysis of the other clinical isolates indicated that the kinetics and ultimate final concentration of Toxin A and B did not correlate with the presence or lack of alterations in tcdC, tcdR or tcdE.

Conclusion: Our data do not support a direct role for alterations in the tcdC gene as a predictor of hyperproduction of Toxin A and B in NAP1-related strains.

Publication types

  • Comparative Study

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism*
  • Bacterial Toxins / metabolism*
  • Bacterial Typing Techniques
  • Caco-2 Cells
  • Clostridium difficile / classification
  • Clostridium difficile / genetics*
  • Clostridium difficile / growth & development
  • DNA, Bacterial / genetics
  • Enterotoxins / metabolism*
  • Gene Expression Regulation, Bacterial
  • Humans
  • Molecular Sequence Data
  • Mutation
  • Repressor Proteins / genetics*
  • Sequence Analysis, DNA


  • Bacterial Proteins
  • Bacterial Toxins
  • DNA, Bacterial
  • Enterotoxins
  • Repressor Proteins
  • TcdC protein, Clostridium difficile
  • tcdA protein, Clostridium difficile
  • toxB protein, Clostridium difficile