Optimized fecal microbiota transplantation using membrane-filtered bacterial concentrates as adjunctive therapy for mild-to-moderate ulcerative colitis: a retrospective cohort study.

Background and aims: Fecal microbiota transplantation (FMT) has emerged as a promising therapeutic approach for ulcerative colitis (UC). This single-center retrospective cohort study evaluated the clinical effectiveness and safety of an optimized FMT protocol, in which donor bacteria were concentrated by tangential-flow micropore membrane filtration and delivered after pre-FMT antibiotic preconditioning, as adjunctive therapy in adults with mild-to-moderate UC. Methods: We analyzed prospectively collected data from 156 patients with mild-to-moderate active UC treated between December 2022 and December 2024. Treatment allocation was determined by a shared clinical decision between the gastroenterologist and patient based on disease severity, prior medication exposure, and patient preference. Patients were grouped into four pre-specified treatment strata: aminosalicylates alone (Group A, Results: Clinical response rates at 12 weeks were 31.0% (Group A), 52.6% (Group B), 72.5% (Group FMT1), and 77.8% (Group FMT2). Clinical remission rates were 19.0%, 34.2%, 55.0%, and 61.1%, respectively. FMT-containing regimens were associated with higher response and remission than aminosalicylates alone (risk difference for response: 41.5%, 95% Conclusions: In this retrospective cohort, an optimized FMT protocol using membrane-filtered bacterial concentrates was associated with higher rates of clinical response, clinical remission and endoscopic improvement at 12 weeks compared with conventional therapy, with an acceptable short-term safety profile. Given the observational design, these findings should be interpreted as hypothesis-generating and require confirmation in randomized controlled trials.