Bacillus subtilis can alleviate visceral hypersensitivity and promote colonic motility in irritable bowel syndrome rats by regulating gut microbiota and promoting synthesis and release of 5-HT

Synthesis and release of 5-hydroxytryptamine (5-HT) plays a critical role in irritable bowel syndrome (IBS). Bacillus subtilis (BS) could regulate gut microbiota and enhance the synthesis of 5-HT in the host colon. Nevertheless, its involvement in the pathogenesis of IBS and its potential as a therapeutic candidate warrant further investigation. In this study, we explored the effects of BS on the phenotype and the synthesis and metabolism of 5-HT in IBS model rats. We found that BS could promote colonic motility and alleviated visceral hypersensitivity in IBS rats. Furthermore, BS restored the composition of intestinal microbiota in IBS rats. Specifically, at the species level, compared to the WAS group, there was a significant increase in the relative abundance of Bacterium D42-87, Acetatifactor muris, Lactobacillus murinus, and there was a significant decrease in the relative abundance of Lactobacillus reuteri in the WAS+BS group. In addition, it was observed that Clostridium sp CAG 510, Clostridium sp CAG 167, Eubacterium xylanophilum and Roseburia sp CAG 309 exhibited the most notable changes in WAS+BS group. By further research, we revealed that BS could increase the number of enterochromaffin cells (ECs), as well as upregulate the expression of 5-HT, TPH1 and 5-HT4R protein in the colon of IBS rats. This study indicate that BS may modulate the composition of intestinal flora, regulate the synthesis and release of intestinal 5-HT, therefore ameliorating Visceral hypersensitivity (VH) and promoting colonic motility in IBS rats.