Abstract
Studies have linked dysbiosis of gut microbiota to irritable bowel syndrome (IBS). However, dysbiosis only referring to structural changes without functional alteration or focusing on luminal microbiota are incomplete. To fully investigate the relationship between gut microbiota and clinical symptoms of Irritable Bowel Syndrome with Diarrhea (IBS-D), fecal samples, and rectal mucosal biopsies were collected from 69 IBS-D patients and 20 healthy controls (HCs) before and during endoscopy without bowel preparation. 16S rRNA genes were amplified and sequenced, and QIIME pipeline was used to process the composition of microbial communities. PICRUSt was used to predict and categorize microbial function. The composition of mucosa-associated microbiota (MAM) was significantly different in IBS-D patients compared to HCs; while no difference in luminal microbiota (LM). MAM, but not LM, was significantly positively correlated with abdominal pain and bloating. A greater number of MAM functional genes changed in IBS-D patients than that of LM compared with HCs. Metabolic alteration in MAM not in LM was related to abdominal pain and bloating. There was a close relationship between the composition and function of MAM and clinical symptoms in IBS-D patients which suggests the important role of MAM in pathogenesis and therapies in IBS-D and it should be highlighted in the future.
Highlights
Irritable bowel syndrome (IBS) is a common gastrointestinal disorder with a high incidence, persistent symptoms, and limited therapeutic options, and greatly affects the quality of life (Ford et al, 2017)
A similar separation was found in mucosa-associated microbiota (MAM) between Irritable Bowel Syndrome with Diarrhea (IBS-D) patients and healthy controls (HCs) (Anosim R = 0.36, P = 0.001); there was no difference in luminal microbiota (LM) between IBS-D patients and HCs (Anosim R = −0.047, P = 0.785) (Figure 1)
We further found that seven functional genes belonged to the 4 metabolic pathways above showed a significant difference between IBS-D patients and HCs in MAM, while only the nitrogen metabolism in IBS-D patients was higher than HCs, the other metabolic pathway did not show any significant difference in LM (Supplementary Figure 1)
Summary
Irritable bowel syndrome (IBS) is a common gastrointestinal disorder with a high incidence, persistent symptoms, and limited therapeutic options, and greatly affects the quality of life (Ford et al, 2017). Studies that have focused on the relationship between luminal microbiota (LM) and IBS have shown inconsistent results (Rajilic-Stojanovic et al, 2011; Carroll et al, 2012b; Jalanka-Tuovinen et al, 2014; Tap et al, 2017). These studies have used a small number of samples. Recent findings on the relationship between mucosal-associated (MAM) and IBS have not reported significant changes in MAM, likely since mucosal specimens are difficult to obtain which limits the number of samples (Carroll et al, 2012a; Rangel et al, 2015; Maharshak et al, 2018). The mixed subtypes of IBS and disruption of MAM caused by bowel preparation can affect results (Rangel et al, 2015)
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