Comparison of the Gut Microbiota of Patients Who Improve with Antibiotic Combination Therapy for Ulcerative Colitis and Those Who Do Not: Investigation by Fecal Metagenomic Analyses

<b>Background/Objectives</b>: The cause of ulcerative colitis (UC) may be related to commensal bacteria in genetically susceptible patients. We previously demonstrated that triple antibiotic combination therapy induces remission in patients with active UC in randomized controlled trials (RCTs). Now, we investigate changes in the gut microbiota of patients who responded to the antibiotic combination therapy. <b>Methods</b>: Thirty-one patients with UC given ATM/AFM (amoxicillin, metronidazole, and tetracycline or fosfomycin) therapy for two weeks were enrolled in this study. The clinical conditions of these UC patients were evaluated by the partial Mayo score. The gut microbiota was compared via the metagenomic shot gun analysis of fecal samples. <b>Results</b>: Of the 31 patients, 16 and 8 experienced complete and partial remission, respectively, over three months in response to ATM/AFM therapy, whereas ATM/AFM showed no efficacy in 7 patients. The dysbiosis before treatment in the active stage could be associated with increased populations of <i>Bacteroides</i>, <i>Parabacteroides</i>, <i>Rickenella</i>, <i>Clostridium</i>, <i>Flavonifractor</i>, <i>Pelagibacter</i>, <i>Bordetella</i>, <i>Massilia</i>, and <i>Piscrickettsia</i> species. Metagenomic analysis revealed dramatic changes in the gut microbiota at an early stage, that is, just two weeks after starting ATM/AFM therapy. After treatment in the responder group, the populations of bifidobacterium and lactobacilli species were significantly increased, while the population of bacteroides decreased. <b>Conclusions</b>: These results suggest that metagenomic analysis demonstrated a marked change in the gut microbiota after antibiotic combination treatment. In the triple antibiotic combination therapy, remission was associated with an increase in bifidobacterium and lactobacilli species.