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Absence of toxin gene transfer from Clostridioides difficile strain 630Δerm to nontoxigenic C. difficile strain
Susan P Sambol1,2, Stuart Johnson1,2, Adam Cheknis1
1Edward Hines, Jr. VA Hospital, Hines, Illinois, United States of America.
Abstract:
Nontoxigenic Clostridioides difficile strain M3 (NTCD-M3) protects hamsters and humans against C. difficile infection. Transfer in vitro of the pathogenicity locus (PaLoc) to nontoxigenic strain CD37 has been reported. We repeated these conjugations using toxigenic strain 630Δerm as donor and NTCD-M3 and CD37 as recipients. In order to conduct these matings we induced rifampin resistance (50ug/ml) in NTCD-M3 by serial passage on rifampin-containing media to obtain strain NTCD-M3r. 630Δerm/CD37 matings produced 21 PaLoc transconjugants in 5.5 x 109 recipient CFUs; a frequency of 3.8 x 10-9. All transconjugants carried the tcdB gene and produced toxin. 630Δerm/NTCD-M3r matings produced no transconjugants in 5 assays with a total of 9.4 x 109 NTCD-M3r recipient cells. Toxin gene transfer to NTCD-M3r could not be demonstrated under conditions that demonstrated transfer to strain CD37.
Insights
Nontoxigenic Clostridioides difficile strain M3 (NTCD-M3) did not acquire toxin genes from a toxigenic strain. This suggests NTCD-M3 may be resistant to toxin gene transfer, unlike other nontoxigenic strains.
Area of Science:
- Microbiology
- Bacterial Genetics
- Infectious Diseases
Background:
- Nontoxigenic Clostridioides difficile strain M3 (NTCD-M3) offers protection against C. difficile infection.
- Previous studies reported successful in vitro transfer of the pathogenicity locus (PaLoc) to nontoxigenic strain CD37.
Purpose of the Study:
- To investigate the susceptibility of NTCD-M3 to toxin gene transfer.
- To compare toxin gene transfer efficiency between NTCD-M3 and CD37.
Main Methods:
- Conjugation experiments were performed using a toxigenic strain (630Δerm) as the donor.
- Nontoxigenic strains NTCD-M3 and CD37 were used as recipients.
- NTCD-M3 was rendered rifampin-resistant (NTCD-M3r) for selection purposes.
Main Results:
- Successful transfer of the PaLoc and toxin production were observed in CD37 transconjugants.
- No PaLoc transconjugants were obtained when using NTCD-M3r as the recipient, even under conditions that allowed transfer to CD37.
- Toxin gene transfer to NTCD-M3r could not be demonstrated.
Conclusions:
- Nontoxigenic Clostridioides difficile strain M3 appears resistant to toxin gene transfer.
- This resistance may contribute to its protective effect against C. difficile infection.
- Further investigation is needed to understand the mechanisms of this resistance.
