BackgroundBariatric surgery is the most effective method of morbid obesity treatment. Microbiota has many functions in human body and many of them remain to be unknown. The aim of this study was to establish if the composition of duodenal microbiota influences success rate of bariatric surgery.MethodsIt was a prospective cohort study. The data concerning demographics and comorbidities was collected perioperatively. The duodenal biopsies were collected prior to surgery with the gastroscope. Then DNA analysis was conducted. The data connected to the operation outcomes was gathered after 6 and 12 months after surgery.ResultsOverall, 32 patients were included and divided into two groups (successful – group 1 and unsuccessful – group 0) based on percentage excess weight loss after 6 months were created. The Total Actual Abundance was higher in group 0. In group 0 there was a significantly higher amount of Roseburia and Arthrobacter (p= 0.024,p= 0.027, respectively). Genus LDA effect size analysis showed Prevotella, Megasphaera and Pseudorhodobacter in group 1 to be significant. Whereas abundance of Roseburia and Arthrobacter were significant in group 0.ConclusionsDuodenal microbiota composition may be a prognostic factor for the success of the bariatric surgery but further research on the larger group is needed.