Background: The gut microbiota is suggested to play an important role in the pathogenesis of ulcerative colitis (UC). However, inter-individual and spatial variations hamper the identification of UC-related changes. We thus investigated paired mucosa-associated microbiota obtained from both inflamed and non-inflamed sites of UC patients and corresponding sites of non-IBD controls. Methods: Mucosal biopsies of both inflamed and non-inflamed sites were obtained from 14 patients with active UC of the left-sided or proctitis type. Paired mucosal biopsies of the corresponding sites were obtained from 14 non-IBD controls. The microbial community structure was investigated using 16S rRNA gene sequences, followed by data analysis using Qiime and LEfSe software. Results: Microbial alpha diversity in both inflamed and non-inflamed sites was significantly lower in UC patients compared with non-IBD controls. There were more microbes of the genus Cloacibacterium and the Tissierellaceae family, and there were less microbes of the genus Neisseria at the inflamed site when compared to the non-inflamed site in UC patients. Decreased abundance of the genera Prevotella, Eubacterium, Neisseria, Leptotrichia, Bilophila, Desulfovibrio, Butyricimonas was evident at the inflamed site of UC patients compared to the corresponding site of non-IBD controls. Among these taxa, the genera Prevotella and Butyricimonas were also less abundant at the non-inflamed site of UC patients compared to the corresponding site in non-IBD controls. Conclusion: Mucosal microbial dysbiosis occurs at both inflamed and non-inflamed sites in UC patients. The taxa showing altered abundance in UC patients might mediate colonic inflammation.
