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

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. 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. The prevalence of SIBO in IBS-D patients was higher than that in healthy controls (51.7% 16.7%,  ≤ .001). In addition, IBS-SSS in SIBO subgroup was significantly higher than SIBO subgroup ( = .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 in IBS-D patients, especially in IBS-D SIBO sufferers. Meanwhile, there were a moderately positive correlation of the abundance of (rho = 0.458,  ≤ .001) with IBS-SSS. SIBO is associated with IBS-D, which may be related to alteration in the intestinal microbiota. These findings suggest the potent role of in gastrointestinal symptoms between SIBO and IBS-D, thus provide a novel insight into the connection between SIBO and IBS-D.