Bifidobacterium longum CCFM760 combined with lactulose alleviates loperamide-induced constipation by regulating the gut microbiota and improving short-chain fatty acid metabolism

Constipation is a prevalent gastrointestinal disorder that severely affects people's daily life and work. <em>Bifidobacterium </em>has been proven to be effective in relieving constipation. Compared with single-strain intervention, the combined intervention of probiotics and oligosaccharides can produce more significant health effects. However, its specific efficacy and mechanism in relieving constipation have not been fully elucidated. This study aims to explore the potential of the synergistic intervention of <em>Bifidobacterium</em> and oligosaccharides in improving constipation, with a particular emphasis on investigating the regulatory effects of the combined intervention on the gut microbiota and its metabolites. In this study, based on the physiological characteristics of the strains and animal experiments, a strain of <em>B. longum </em>CCFM760 capable of relieving constipation was screened. Furthermore, nine kinds of oligosaccharides were used to replace glucose as the single carbon source respectively. According to the shortest generation time of the strain, lactulose was selected as the compounding factor to investigate how the combined intervention of <em>B. longum</em> CCFM760 and lactulose relieves constipation and reveal the involved mechanisms. It was shown that compared with the single-strain intervention, the combined intervention therapy could better relieve constipation. By promoting the intestinal colonization of <em>Bifidobacterium</em>, it could more significantly reduce the relative abundances of harmful bacteria such as <em>Bilophila</em> and <em>Negativibacillus</em>, and at the same time significantly enrich short-chain fatty acids (SCFAs)-producing bacteria such as <em>Bifidobacterium</em>, <em>Faecalibaculum</em>, and <em>Ileibacterium</em>. Therefore, it could more effectively restore the levels of SCFAs in the gut, increase the expression level of serotonin 4 receptor (5-HT4R), improve the levels of gastrointestinal active peptides (increasing the levels of gastrin (GAS) and motilin (MTL), and decreasing the level of vasoactive intestinal peptide (VIP)), as well as the expression levels of calcitonin gene-related peptide (CGRP) and brain derived neurotrophic factor (BDNF), and reduce the expressions of Aquaporin-3 (AQP3) and inducible nitric oxide synthase (iNOS) in the colon tissue, thus more effectively relieving constipation. These results lay the foundation for the development of dietary formula foods with the efficacy of relieving constipation.