Ulcerative colitis (UC) is a chronic immune-mediated inflammatory bowel disease (IBD) that almost always affects the rectum and often extends to the more proximal colon. UC usually begins at a young age (15-30 years), most patients (~ 85%) have a mild or moderate activity, characterized by periods of exacerbation and remission. Considering the important pathogenetic role of gut dysbiosis, recently, as an additional method of treating UC, it is considered a modification of altered gut microbiota using various drug and non-drug methods. One such method is fecal microbiota transplantation (FMT), consisting of the simultaneous replacement of the gut microbiota of a sick recipient with fecal material from a healthy donor. Even though so far the only officially approved indication for FMT is recurrent Clostridium difficile infection, however, the effectiveness of FMT is currently being studied in the treatment of other gastrointestinal and non-gastrointestinal pathologies, including UC. To date, several controlled and uncontrolled studies have been conducted to study the effectiveness of FMT in UC, showing encouraging results. This study aimed to assess the clinical and microbiological efficacy, tolerability, and safety of FMT as add-on therapy to basic therapy, in patients with mild-to-moderate UC.

Inclusion Criteria:

• Age 18-60;
• Endoscopically and morphologically confirmed UC;
• Negative results of stool culture for the presence of pathogenic bacteria (Shigella spp., Salmonella spp., Campylobacter spp., Yersinia spp.) and toxin-producing Clostridioides difficile;
• partial Mayo score of 4-6;
• Mayo endoscopic subscore ≥1;
• Fecal calprotectin > 150 mcg/g
• Treatment with mesalazine at a daily dose of 3 g during the last 4 weeks

Exclusion Criteria:

• Pregnancy, planning pregnancy or breastfeeding;
• Postponed operations on the abdominal cavity;
• Severe mental disorders, alcohol or drug abuse;
• Use of systemic corticosteroids, biological agents, and probiotics within 8 weeks before study
• Any condition or circumstance that would, in the opinion of the investigator, prevent completion of the study or interfere with analysis of study results.