Objective Clostridium difficile is a toxin-producing bacterium and a leading cause of antibiotic-associated disease. The ability of C. difficile to form spores and infect antibiotic-treated persons at low multiplicity of infection (MOI) underlies its large disease burden. However, C. difficile-induced disease might also result from long-harboured C. difficile that blooms in individuals administered antibiotics.
Design Mice purchased from multiple vendors and repeatedly testing negative for this pathogen by quantitative PCR bloomed C. difficile following antibiotic treatment. This endogenous C. difficile strain, herein termed LEM1, which formed spores and produced toxin, was compared with highly pathogenic C. difficile strain VPI10463.
Results Whole-genome sequencing revealed that LEM1 and VPI10463 shared 95% of their genes, including all known virulence genes. In contrast to VPI10463, LEM1 did not induce overt disease when administered to antibiotic-treated or germ-free mice, even at high doses. Rather, blooms of LEM1 correlated with survival following VPI10463 inoculation, and exogenous administration of LEM1 before or shortly following VPI10463 inoculation prevented C. difficile-induced death. Accordingly, despite similar growth properties in vitro, LEM1 strongly outcompeted VPI10463 in mice even at 100-fold lower inocula.
Conclusions These results highlight the difficulty of determining whether individual cases of C. difficile infection resulted from a bloom of endogenous C. difficile or a new exposure to this pathogen. In addition to impacting the design of studies using mouse models of C. difficile-induced disease, this study identified, isolated and characterised an endogenous murine spore-forming C. difficile strain able to decrease colonisation, associated disease and death induced by a pathogenic C. difficile strain.
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Contributors LE-M, BC and ATG designed the experiments. LE-M, BC and OA performed the experiments. LE-M, BC and ATG analysed and interpreted data. LMM performed whole-genome sequencing and bioinformatics analysis. LE-M and ATG wrote the manuscript with input from coauthors. LE-M., BC, OA, LMM, FDB and ATG critically revised the manuscript.
Funding This work was supported by National Institutes of Health grants DK099071 and DK083890 to ATG. BC is a recipient of the Career Development Award from the Crohn's and Colitis Foundation of America.
Competing interests None declared.
Ethics approval All animals were housed at Georgia State University (Atlanta, Georgia, USA). All procedures were performed under institutionally approved animal use (Georgia State University Institutional Animal Care and Use Committee, IACUC protocol number A14033) whose responsibilities are mandated by the Animal Welfare Act (Public Law 98–198), Guide for Care and Use of Laboratory Animals and Public Health Service Policy on Humane Care and Use of Laboratory Animals.
Provenance and peer review Not commissioned; externally peer reviewed.
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