Lactobacillus paracasei from koumiss mediates intestinal stem cells to promote intestinal mucosal recovery through intestinal microbiota-metabolites

Background Infectious diarrhea caused by Salmonella typhimurium ( S. typhimurium ) leads to intestinal barrier dysfunction, dysbiosis, and impaired epithelial regeneration. Current antibiotic therapies are prone to adverse effects such as drug resistance and drug residues, whereas probiotic interventions have shown beneficial effects. In this context, the study focused on a traditional fermented product called koumiss, from which a strain of Lactobacillus paracasei ( L. paracasei ) was isolated. Previous studies have demonstrated that this strain is capable of repairing the damaged intestinal mucosal barrier. However, its underlying mechanism of action remains unclear. Methods Seventy Kunming mice were randomly divided into control group, model group, L. paracasei intervention group, and Lactobacillus plantarum ( L. plantarum ) intervention group. Except for the control group, the diarrhea model induced by S. typhimurium was established in the other groups. Serum inflammatory factors, intestinal permeability, and immune indexes were detected by enzyme-linked immunosorbent assay. Hematoxylin eosin, Alcian blue-periodic acid–Schiff, electron microscopy, immunofluorescence, reverse transcription quantitative polymerase chain reaction, and Western blot were used to evaluate the intestinal barrier function and the ability of intestinal stem cells to proliferate and differentiate into Paneth cells and goblet cells. The structure of the intestinal flora and the content of short-chain fatty acids (SCFAs) were detected by 16S ribosomal ribonucleic acid, and gas chromatography–mass spectrometry. Furthermore, fecal microbiota transplantation was performed by transferring feces from L. paracasei -intervened mice to germ-free mice, in order to determine whether the microbiota reshaped by L. paracasei could independently mediate intestinal repair and to verify the interaction between the microbiota and metabolites. Results L. paracasei and L. plantarum can significantly reduce diarrhea symptoms, weight loss, and intestinal barrier damage, reduced serum lipopolysaccharide, diamine oxide, D-lactate, and zonulin levels, promote the expression of tight junction proteins, and promote the proliferation and differentiation of Lgr5 + intestinal stem cells, increased the expression of Paneth cells (lysozyme, Defa5, Ang4) and goblet cells (MUC2, TFF3) markers, and enhanced the protective effect of the physical mucus barrier on the intestine, but the protective effect of L. paracasei on the intestinal mucosa is better than that of L. plantarum . 16S rRNA sequencing showed that compared with L. plantarum , L. paracasei intervention enriched the Muribaculaceae and Prevotellaceae families that produced SCFAs. The results of fecal microbiota transplantation showed that the transplantation of L. paracasei in the feces of mice still had the protective effect of intestinal mucosal barrier, which could restore the expression of intestinal stem cells, improve the intestinal mucosal barrier, reduce inflammation and increase the level of SCFAs, indicating that L. paracasei mediated the repair of intestinal mucosal barrier damage through intestinal microbiota-metabolites. Conclusion Both L. paracasei and L. plantarum are capable of repairing intestinal injury, however, L. paracasei is proved better than L. plantarum . L. paracasei ameliorates infectious diarrhea by remodeling the gut microbiota, enhancing production of SCFAs, suppressing inflammation, preserving Paneth cell niche function, and ultimately promoting Lgr5 + intestinal epithelium and stem cell (ISC)-mediated epithelial regeneration. These findings provide a mechanistic basis for probiotic intervention in infectious diarrhea and highlight the microbiota–ISC axis as a therapeutic target.