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

Background: 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 levels and antimicrobial activity were monitored throughout the experiment. Results: Both C. difficile strains germinated and proliferated in response to ceftriaxone instillation, with cytotoxin detected during the peak vegetative growth. Vancomycin instillation resulted in a rapid decline in the vegetative forms of both strains, with only spores remaining 2 days after the start of dosing. A recrudescence of both strains occurred following the cessation of vancomycin installation, although this was observed more quickly, and to a greater extent, in one strain than the other. Conclusions: Within a human gut model, multiple C. difficile strains are able to germinate and proliferate con-currently in response to antibiotic challenge (the onset of simulated CDI). Similarly, more than one strai