Lactobacillus spp. can be beneficial for the prevention or treatment of ulcerative colitis (UC). In this study, 153 participants who followed vegan, omnivorous, or high-meat diet were recruited. Compositional analysis of the Lactobacillus community in feces revealed that Lactobacillus fermentum strains were significantly affected by diet. Administration of mixed L. fermentum strains from vegans significantly improved inflammation compared to that from omnivores and high-meat consumers, as evidenced by a significant reduction in colonic tissue damage, improvement in inflammatory cytokines, enhanced expression of ZO-1, occludin, and claudin-3, and a significant increase in short chain fatty acids concentration. The effect of a single strain of L. fermentum was similar to that of a mixed strains of L. fermentum group. Genomic analysis suggested that L. fermentum strains from the guts of vegans possessed a higher prevalence of genes involved in carbohydrate catabolism than those from the guts of omnivores and high-meat eaters. In particular, the ME2 gene is involved in the biosynthesis of acetate, a compound considered to possess anti-inflammatory properties. In conclusion, this study indicates strain-specific differences in the ability of L. fermentum strains to alleviate UC in mice, influenced by habitual diets.

Irritable bowel syndrome-diarrhea (IBS-D) is a prevalent functional bowel disease severely impairs the quality of life of patients. Visceral hypersensitivity (VH) is the main symptom of IBS-D. Probiotics have been found to effectively alleviate VH. In this study, neonatal maternal separation (NMS) was used to induce VH in 72 rats and investigated the effects of daily gavage of 3*10⁹ CFU of Lactobacillus and Bifidobacterium on alleviating the symptoms of IBS-D and behavioral interventions, as well as exploring potential mechanisms. The results demonstrated that Lactobacillus acidophilus and Bifidobacterium breve could alleviate the symptoms of IBS-D such as VH and increased frequency of bowel movements, as well as improving non-spatial memory in NMS rats. These effects were achieved by modulating the composition of gut microbiota and metabolites (including short-chain fatty acids, deoxycholic acid and adenosine), and by regulating the expression of genes and proteins associated with the NGF/TrkA signaling pathway, tryptophan metabolism, and inflammatory factors in the hippocampus. This finding suggests that Lactobacillus acidophilus and Bifidobacterium breve have promising potential for the alleviation of IBS.