Differences in clinical manifestations and the fecal microbiome between irritable bowel syndrome and small intestinal bacterial overgrowth

Irritable bowel syndrome (IBS) and small intestinal bacterial overgrowth (SIBO) share similar abdominal symptoms; however, their differentiation remains controversial. To illustrate the differences between the two conditions. Patients and healthy controls completed questionnaires and provided stool samples for analysis. IBS presented with the most severe symptoms and was specifically characterized by intense abdominal pain and frequent episodes of diarrhea. Patients with IBS displayed more dysregulated taxonomy within the fecal microbiota than SIBO. Opportunistic pathogens, including Lachnoclostridium, Escherichia-Shigella, and Enterobacter were enriched in the IBS group which contributed to increased bacterial pathogenicity and positively correlated with abdominal pain and bloating, meanwhile, Lachnoclostridium and Escherichia-Shigella were found to be associated with metabolites affiliated to bile acids, alcohols and derivatives. Bacteria enriched in SIBO group correlated with constipation. The bacterial co-occurrence network within the SIBO group was the most intricate. Ruminococcaceae Group were defined as core bacteria in SIBO. Differential metabolites affiliated to androstane steroids and phenylacetic acids were associated with core bacteria. Our study elucidates the differences between IBS and SIBO in terms of symptoms, microbiota and functions, which provides insights into a better understanding of both diseases and evidence for different treatment strategies.