Phenotypic, Genomic, and In Vivo Characterization of a Host-Derived Limosilactobacillus fermentum RLF77 with Potential to Prevent Post-weaning Diarrhea in Rabbits.

Following the 2020 ban on antibiotic growth promoters in animal feed, diarrheal disease in weaned rabbits has become an increasingly important challenge for the rabbit industry. Due to their superior intestinal adaptability and colonization potential, host-derived probiotics are considered promising alternatives. In this study, Limosilactobacillus fermentum RLF77, a lactic acid bacterium, was isolated from the intestinal contents of healthy young rabbits. Strain RLF77 showed a favorable safety profile, including γ hemolysis, a negative indole reaction, and no production of biogenic amines. Furthermore, the strain exhibited strong tolerance to heat, acidic conditions, bile salts, and simulated gastrointestinal fluids, as well as broad antimicrobial activity against a range of enteric pathogens. It also displayed moderate cell surface hydrophobicity, auto-aggregation ability, and strong antioxidant activity. Whole genome sequencing revealed that RLF77 possesses a 2.31 Mbp genome enriched in genes involved in carbohydrate and amino acid metabolism, stress response, and oxidative defense. In addition, genome mining identified biosynthetic gene clusters putatively encoding enterolysin A. Oral administration in mice further supported the in vivo safety of RLF77 and significantly increased villus height and the villus height/crypt depth ratio. In an E. coli-challenged weaned rabbit model, dietary RLF77 supplementation improved growth performance, reduced diarrhea incidence, enhanced immune and antioxidant capacity, alleviated intestinal injury, and improved gut microbiota composition by increasing microbial richness and Akkermansiaceae abundance. Collectively, the host-derived strain L. fermentum RLF77 is a safe and promising probiotic candidate for improving intestinal health and preventing post-weaning diarrhea in rabbits.