Bioactive Low-Molecular-Weight Fraction from Limosilactobacillus fermentum CECT5716 Attenuates Intestinal Inflammation and Dysbiosis in DSS-Treated Mice.

Postbiotics, including cell-free supernatants and their fractions, have emerged as a safe and effective alternative to live probiotics for managing intestinal inflammation. This study investigated the protective effects of low-molecular-weight fractions (<3 kDa) of the probiotic Limosilactobacillus fermentum CECT5716 (LMW-LF) in a murine model of experimental colitis. Male C57BL/6J mice were orally administered LMW-LF for 10 days prior to colitis induction with 3% dextran sodium sulfate (DSS) for 5 days. Colonic damage was assessed via the Disease Activity Index (DAI), histology, and immunofluorescence (Ocln and Ki67). Immune cell populations were analyzed by flow cytometry, while mucosal gene expression and gut microbiota composition were evaluated using RT-qPCR and 16S rRNA sequencing, respectively. LMW-LF administration significantly attenuated clinical symptoms and macroscopic colonic damage. Treatment restored epithelial barrier integrity by upregulating tight junction proteins (Tjp1) and mucin genes (Muc1-3) while normalizing DSS-induced epithelial hyperproliferation. Immunologically, LMW-LF reduced pro-inflammatory monocyte infiltration; downregulated Il6, Tnfa, and Ifng; and promoted an immunoregulatory phenotype by enhancing Ampk expression and partially restoring regulatory T cell (Treg) populations. Furthermore, LMW-LF reshaped the gut microbiota by increasing alpha diversity and promoting the enrichment of beneficial taxa, specifically Akkermansia muciniphila, which correlated with improved mucus layer preservation. LMW-LF is an active fraction acting across the host-microbiota axis. By integrating epithelial protection, immunomodulation, and microbial reshaping, it represents a promising dietary strategy for the management of Inflammatory Bowel Diseases.