A Hensen, Céline Harmanus, P. H. Verbeek-Menken, Jan Pieter R. Koopman, O. A. C. Lamers, Geert V.T. Roozen, Jacqueline J. Janse, M. Balke-Buijs, M. Y. E. C. van der Stoep, Pauline Meij, I.M. van Amerongen-Westra, P. Schipper, C. Crul, L. Pattacini, Katharina Rox, F. Farowski, Anastasia Tsakmaklis, M.J.G.T. Vehreschild, Ed J. Kuijper, Wiep Klaas Smits, Meta Roestenberg
Clostridioides difficile infections remain a major global healthcare burden, underscoring the need for novel therapies. Human colonisation models provide mechanistic insight into C. difficile colonisation and facilitate identification of novel intervention targets. We conducted a placebo-controlled, randomised clinical trial (NCT05693077) administering non-toxigenic C. difficile (NTCD) capsules to healthy participants to assess safety and colonisation as primary endpoints, and microbiota susceptibility as a secondary endpoint. A total of 69 healthy participants (18-45 years), not previously colonised with C. difficile and without recent antibiotic use, were enrolled following a health assessment. NTCD capsules administered for five consecutive days at low or high dose, was safe with no dose-response relationship in colonisation outcomes. Vancomycin pretreatment induced colonisation success: with 5% colonisation without, 32% after one day, and 84% after five days vancomycin pretreatment. Some participants that cleared vancomycin rapidly acquired non-challenge C. difficile strains prior to NTCD challenge. Microbiota profiling (using shotgun metagenomics) revealed reduced α-diversity and pronounced community restructuring. These findings highlight the impact of antibiotic-mediated microbiota disruption, the widespread environmental presence of C. difficile, and the feasibility of meaningful microbiota assessment in small-scale intervention trials, thereby providing a robust tool to investigate this globally impactful infection.