Fecal microbiota profiling in patients with irritable bowel syndrome and small intestinal bacterial overgrowth

Small intestinal bacterial overgrowth (SIBO) is common in irritable bowel syndrome (IBS) and has been proposed as an etiologic factor. This study aimed to identify potential fecal microbiota profiles in patients with IBS and SIBO. A total of 52 subjects were enrolled in this study, of whom 18 were normal controls (NCs). Patients were divided into 2 groups: IBS with SIBO (IBS.SIBO+) and IBS without SIBO (IBS.SIBO−). SIBO was identified using a standard glucose hydrogen breath test. The IBS symptom severity scale, abdominal pain, and health-related quality of life were evaluated using questionnaires. Rectal balloon distension was used to measure visceral sensitivity. Fresh fecal samples were collected, and 16S rRNA gene sequencing analysis was performed to evaluate the structure and diversity of the microbiota among different groups. Correlation analysis was performed to assess the relationship between specific flora and abdominal pain, visceral sensitivity, and quality of life. The richness of the intestinal microbiota in the IBS.SIBO− group was significantly lower than that in the IBS.SIBO+ group ( P  = .012). At the phylum level, the relative abundance of Firmicutes decreased significantly in fecal samples collected from IBS with SIBO compared to those in the NCs and IBS without SIBO groups. No significant difference was found between the NCs and IBS without SIBO groups, although the phylum type showed a decreasing trend in the latter. At the genus level, Fusobacterium (P  = .01) was significantly less abundant in the IBS with SIBO group than in the NC group; however, no significant difference was found between the IBS with SIBO and IBS without SIBO groups. The relative abundance of Firmicutes correlated negatively with the abdominal pain scale ( r  = 0.436, P  = .026) and the IBS symptom severity scale ( r  = 0.494, P  = .010), whereas a positive correlation was found between the defecation distress threshold and Firmicutes (r  = 0.458, P  = .019). Fecal microbiota showed mild dysbiosis in patients with IBS and SIBO compared to those without SIBO. The decreased abundance of Firmicutes may be related to IBS symptoms and abdominal pain.