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Open Access Highly Accessed Research article

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

Ruth Murray14, Dave Boyd2, Paul N Levett3, Michael R Mulvey2 and Michelle J Alfa4*

  • * Corresponding author: Michelle J Alfa

  • † Equal contributors

Author Affiliations

1 St. Boniface Research Centre, Winnipeg, MB, Canada

2 Public Health Agency of Canada, Winnipeg, MB, Canada

3 Public Health Agency of Canada, Saskatchewan, Canada

4 Department of Medical Microbiology, University of Manitoba, Winnipeg, MB, Canada

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BMC Infectious Diseases 2009, 9:103  doi:10.1186/1471-2334-9-103

Published: 28 June 2009



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.


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.


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.


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.