Enterococcus hirae QT4713 alleviated DSS-induced colitis by modulating gut microbiota and tryptophan metabolism in mice

Probiotics are known to alleviate inflammatory bowel disease, and their precise mechanisms remain unclear. In this study, we identified a strain of Enterococcus hirae QT4713, isolated from the Tibetan plateau, that exhibited high anti-inflammatory activity in vitro. After confirming its tolerance to gastrointestinal fluids and safety, we evaluated the effect of E. hirae QT4713 on IBD using a dextran sulfate sodium (DSS)-induced colitis mouse model and analyzed the microbial response through metagenomic and metabolomics. The results indicated that E. hirae QT4713 alleviated colitis symptoms by reducing oxidative stress in the serum and inflammatory cytokine levels in colonic tissue, particularly IL-1β (P < 0.05). It also reduced structural damage, inflammatory infiltration, and epithelial cell apoptosis in the colon. Additionally, the strain increased the expression of MUC-2 and occludin in colonic tissue, which helped to protect the colonic barrier. Furthermore, intervention with E. hirae QT4713 enriched beneficial bacteria such as Bifidobacteria and Lactobacillus, increased the levels of butyric acid and propionic acid in the gut (P < 0.05), regulated tryptophan metabolism, and promoted the production of its indole derivatives, including 3-indoleacetonitrile, 3-indoleacrylic acid, and indole-3-lactic acid (P < 0.05), thus alleviating colitis. These findings provide new insights into how probiotics, such as E. hirae QT4713, alleviated colitis in a gut microbiota/tryptophan metabolism-dependent manner.