Pinto, SusanneŠajbenová, DominikaBenincà, ElisaNooij, SamTerveer, Elisabeth MKeller, Josbert Jvan der Meulen-de Jong, Andrea EBogaards, Johannes ASteyerberg, Ewout W2025-02-262025-02-262025-02-043922549010.1093/ecco-jcc/jjae137https://rivm.openrepository.com/handle/10029/628390Fecal microbiota transplantation (FMT) is an experimental treatment for ulcerative colitis (UC). We aimed to study microbial families associated with FMT treatment success.We analyzed stools from 24 UC patients treated with 4 FMTs weekly after randomization for pretreatment during 3 weeks with budesonide (n = 12) or placebo (n = 12). Stool samples were collected 9 times pre-, during, and post-FMT. Clinical and endoscopic response was assessed 14 weeks after initiation of the study using the full Mayo score. Early withdrawal due to worsening of UC symptoms was classified as non-response.Nine patients (38%) reached remission at week 14, and 15 patients had a partial response or non-response at or before week 14. With a Dirichlet multinomial mixture model, we identified 5 distinct clusters based on the microbiota composition of 180 longitudinally collected patient samples and 27 donor samples. A Prevotellaceae-dominant cluster was associated with poor response to FMT treatment. Conversely, the families Ruminococcaceae and Lachnospiraceae were associated with a successful clinical response. These associations were already visible at the start of the treatment for a subgroup of patients and were retained in repeated measures analyses of family-specific abundance over time. Responders were also characterized by a significantly lower Simpson dominance compared to non-responders.The success of FMT treatment of UC patients appears to be associated with specific gut microbiota families, such as control of Prevotellaceae. Monitoring the dynamics of these microbial families could potentially be used to inform treatment success early during FMT.The study was registered in the Netherlands Trial Register, with reference number NL9858.en© The Author(s) 2024. Published by Oxford University Press on behalf of European Crohn’s and Colitis Organisation.Gut microbiotafecal microbiota transplantationulcerative colitisArticleJ Crohns Colitis 2025; 19(2):jjae1377748263