Background: Clostridioides difficile (C. difficile) remains the leading cause of healthcare-associated diarrhoea, posing treatment challenges due to antibiotic resistance and high relapse rates. Fecal microbiota transplantation (FMT) is a novel treatment strategy to prevent relapses of C. difficile infection (CDI), however the exact components conferring colonisation resistance are unknown, hampering its translation to a medicinal product. Development of novel products independent of antibiotics, which increase colonisation resistance or induce protective immune mechanisms are urgently needed.  

Objectives: To establish a framework for a Controlled Human Infection Model (CHIM) for C. difficile, in which healthy volunteers are exposed to toxigenic C. difficile spores, offering the possibility to test novel approaches and identify microbiota and immunological targets. Whereas experimental exposure to non-toxigenic C. difficile (NTCD) has been done before, a toxigenic C. difficile CHIM faces ethical, scientific, logistical and biosafety challenges.

Sources: Specific challenges in developing a C. difficile CHIM were discussed by a group of international experts during a workshop organized by Inno4Vac, an IHI-funded consortium.

Content: The experts agreed that the main challenges are: developing a clinically relevant CHIM which induces mild to moderate CDI symptoms but no severe CDI, determining optimal C. difficile inoculum dose and understanding the timing and duration of antibiotic pre-treatment in inducing susceptibility to CDI in healthy volunteers.

Implications: Should these challenges be tackled, a C. difficile CHIM not only provides a way forward for the testing of novel products but also offers a framework for better understanding of the pathophysiology, pathogenesis and immunology of C. difficile colonisation and infection.