Dietary supplementation with chicken-derived <i>L. rhamnosus</i> CIQ249 protects broilers against enteropathogens by regulating intestinal homeostasis

Lacticaseibacillus rhamnosus is commonly used to manage gastrointestinal infections in children, yet its efficacy as a probiotic feed additive for poultry against enteropathogenic bacteria remains insufficiently explored. In this study, a strain L. rhamnosus (CIQ249) was isolated from chicken intestine and evaluated for its ability to enhance intestinal homeostasis and confer resistance against enteropathogens using chicks as animal model. CIQ249 exhibited strong potential for intestinal colonization and high tolerance to gastrointestinal stress, including acid, bile, and osmotic pressure. In vitro, CIQ249 showed effective inhibitory activity against pathogenic bacteria as determined by agar well diffusion assay. During a one-month feeding trial, dietary supplementation with CIQ249 significantly improved the growth performance of broilers. In subsequent experimental challenges, oral gavage administration of CIQ249 conferred protection against E. coli O78 and S. Typhimurium. Furthermore, CIQ249 modulated intestinal immune response by increasing levels of IL-4, IL-10, IFN-γ, and sIgA, while suppressing production of pro-inflammatory cytokines (IL-6, IL-1β, and TNF-α). It also upregulated expression of tight junction proteins (ZO-1 and Claudin-1), alleviating gut damage induced by pathogenic infections. These findings indicate that CIQ249 is a promising probiotic feed additive that protects chickens from enteropathogenic bacteria by reinforcing intestinal epithelial barrier and enhancing immune homeostasis.