Abstract. Currently, inflammatory bowel diseases with an autoimmune type of lesion (ulcerative colitis, Crohn’s disease) occupy a leading position among gastrointestinal tract (GIT) pathologies. Changes in the generic composition of the intestinal microbiota may be an early diagnostic sign of autoimmune inflammation.
The aim: to assess the biodiversity of the gut microbiota in patients with ulcerative colitis (UC). Material and methods. 16s-RNA genetic sequencing (the main method for studying intestinal microbiota) was carried out on 40 persons – 20 patients with UC of varying severity (main group) and 20 somatically healthy individuals (control group). In all patients, the diagnosis of UC was previously verified accordingly to the results of colonoscopy and targeted biopsy followed by histological examination. The severity of the course of UC was identified by Mayo index. In addition, laboratory diagnostics was carried out. It contained the estimation of indexes of general and biochemical (CRP) blood tests in both study groups. The average age of examined patients was 42±3,5 years.
Results. When assessing laboratory parameters, patients with UC showed leukocytosis (11,4±0,68 g/l), as well as an increase in CRP (9,6±1,5 mg/l) comparatively to the control group. When interpreting Mayo index, most patients had an average severity of the underlying disease. As a result of sequencing of the intestinal microbiota in the main group, comparatively to the control one, a significant decrease in representatives of the normal intestinal microflora – the main producers of short-chain fatty acids, and an increase in bacteria of the pathogenic cluster and sulfate-reducing bacteria were revealed.
Conclusion. A significant decrease in normal microflora and an increase in the pathogenic cluster of bacteria in patients with UC were found. The obtained data can form the basis for improving the diagnosis of this pathology.

Keywords: Mayo index, intestinal microbiota, ulcerative colitis, inflammatory bowel disease