Recurrence of dual-strain Clostridium difficile infection in an in vitro human gut model

Objectives: Clostridium difficile infection (CDI) is still a major challenge to healthcare facilities. The detection of multiple C. difficile strains has been reported in some patient samples during initial and recurrent CDI episodes. However, the behaviour of individual strains and their contribution to symptomatic disease is unclear. Methods: An in vitro human gut model was used to investigate the germination and proliferation of two distinct C. difficile strains during initial and recurrent simulated CDI, as well as their response to vancomycin treatment. The gut model was inoculated with a pooled human faecal emulsion and indigenous gut microbiota, C. difficile populations (vegetative and spore forms), cytotoxin and antimicrobial activity was monitored throughout the experiment. Results: Both C. difficile strains germinated and proliferated in response to ceftriaxone instillation, with cytotoxin detection during peak vegetative growth. Vancomycin instillation resulted in a rapid decline in vegetative forms of both strains, with only spores remaining 2 days after dosing commencement. Recrudescence of both strains occurred following cessation of vancomycin, although this was observed in one strain sooner, and to a greater extent, than the other strain. Conclusions: Within a human gut model multiple C. difficile strains are able to germinate and proliferate concurrently in response to antibiotic challenge (onset of simulated CDI). Similarly, more than one strain can proliferate during simulated recurrent CDI, although with differences in germination and growth rate and timing. It appears probable that multiple strains can contribute to CDI within an individual patient with possible implications for management and bacterial transmission.