Small intestinal bacterial overgrowth is associated with Diarrhea-predominant irritable bowel syndrome by increasing mainly Prevotella abundance.

Objective: Diarrhea-predominant irritable bowel syndrome (IBS-D) is the main subtype of IBS, a chronic functional gastrointestinal disorder. Small intestinal bacterial overgrowth (SIBO), which is characterized by dysbiosis of the bowel, causes gastrointestinal symptoms quite similar to IBS-D. However, whether SIBO correlates with IBS-D and its further mechanism remain unknown. Materials and Methods: The study included 60 IBS-D patients that fulfilled Rome IV criteria and 60 healthy controls. All subjects were undergoing a lactose breath test (LBT) to diagnose SIBO. IBS-D patients were further assigned to negative SIBO (SIBO-) subgroup and positive SIBO (SIBO+) subgroup to analyze the scores of symptoms and differences in the fecal microbiota. Results: The prevalence of SIBO in IBS-D patients was higher than that in healthy controls (51.7% vs. 16.7%, p <= .001). In addition, IBS-SSS in SIBO+ subgroup was significantly higher than SIBO- subgroup (p = .015). The 16S rRNA analyses showed that composition and abundance of fecal microbiota were obviously different between the two subgroups. There was a remarkable increase in Prevotella in IBS-D patients, especially in IBS-D SIBO+ sufferers. Meanwhile, there were a moderately positive correlation of the abundance of Prevotella (rho = 0.458, p <= .001) with IBS-SSS. Conclusion: SIBO is associated with IBS-D, which may be related to alteration in the intestinal microbiota. These findings suggest the potent role of Prevotella in gastrointestinal symptoms between SIBO and IBS-D, thus provide a novel insight into the connection between SIBO and IBS-D.