Mucosa-associated microbiota dysbiosis in the terminal ileum correlates with bowel symptoms in diarrhea-predominant irritable bowel syndrome

Abstract

Abstract Background and aims: The mucosa-associated microbiota (MAM) is not as frequently studied in diarrhea-predominant irritable bowel syndrome (IBS-D) compared to the fecal microbiota. Here, we examined the MAM in the terminal ileum and its correlation with bowel symptoms in IBS-D. Methods: Mucosal biopsies of the terminal ileum from 25 IBS-D patients and 25 healthy controls (HCs) were collected for 16S ribosomal RNA (rRNA) gene sequencing. Correlation analysis was performed. Results: Compared to HCs, the MAM in the terminal ileum showed a decreased alpha-diversity in the IBS-D cohort (Chao1 and Shannon indexes, P < 0.05). And the overall MAM profile clustered separately in two groups (ADONIS, P < 0.05). At the phylum level, the relative abundance of Proteobacteria was significantly higher in the ileal MAM of patients with IBS-D while that of Firmicutes was significantly lower. At the genus level, the relative abundance of Pseudomonas was significantly higher in the IBS-D cohort, with lower Bacteroides and Ruminococcus. Moreover, 40.0% of IBS-D patients had multiple small nodules (nodular lymphoid hyperplasia, NLH) on the mucosal surface of the terminal ileum, which indicated a low-grade inflammation. In the IBS-D patients with NLH, the changes of Pseudomonas and Bacteroides were more overt. Correlation analysis revealed that the relative abundance of Pseudomonas positively correlated with abdominal pain and the severity of IBS. Conclusion: IBS-D patients showed a dysbiosis of MAM in the terminal ileum, which may be associated with bowel symptoms. Moreover, 40.0% of them displayed mucosal low-grade inflammation, with a more severe mucosal microbial disturbance.