Altered gut microbiota in patients with small intestinal bacterial overgrowth

Background and Aim Small intestinal bacterial overgrowth (SIBO) is diagnosed by using quantitative culture of duodenal aspirates and/or a hydrogen breath test. However, few studies have analyzed bacterial microbiota in Japanese patients with SIBO. Methods Twenty-four patients with any abdominal symptoms and suspected SIBO were enrolled. Quantitative culture of duodenal aspirates and a glucose hydrogen breath test were performed on the same day. SIBO was diagnosed based on a bacterial count >= 10(3) CFU/mL or a rise in the hydrogen breath level of >= 20 ppm. The composition of the duodenal microbiota was analyzed by 16S rRNA gene sequencing. Results Small intestinal bacterial overgrowth was diagnosed in 17 of the 24 patients (71%). The positive rates for the hydrogen breath test and quantitative culture of duodenal aspirates were 50% and 62%, respectively. Patients with SIBO showed significantly reduced alpha-diversity compared with non-SIBO patients, and analysis of beta-diversity revealed significantly different distributions between SIBO and non-SIBO patients. In addition, the intestinal microbiome in SIBO patients was characterized by increased relative abundance of Streptococcus and decreased relative abundance of Bacteroides compared with non-SIBO patients. Conclusions Duodenal dysbiosis was identified in patients with SIBO and may play a role in the pathophysiology of SIBO.