Lactic acid bacteria CNCM I-4622 modulates gut microbiota and restores barrier function in Salmonella-infected Haidong chickens

The gastrointestinal tract regulates nutrient absorption and immune homeostasis in poultry.Salmonella infection severely impairs intestinal barrier function, induces systemic inflammation, and disturbs microbial balance, representing a major challenge for the poultry industry.Excessive antibiotic use further contributes to antimicrobial resistance, increasing the demand for safe alternative strategies.Although Lactobacillus confers gut-protective properties, its effects against Salmonella-induced caecal damage in Haidong chickens remain poorly defined.This study aimed to evaluate the protective effects of dietary supplementation with Lactobacillus CNCM I-4622 on caecal function, inflammation, digestive metabolism, and gut microbiota in Salmonella-challenged Haidong chickens.A Salmonella infection model was established, and birds were allocated to a Salmonella-infected group (SIG), a Lactobacillus CNCM I-4622-treated infected group (LTG), and a normal control group (NDG).Samples were analysed using biochemical assays, histomorphometry, qRT-PCR, and 16S rRNA sequencing.Compared to the SIG group, Lactobacillus CNCM I-4622 significantly increased serum total protein, immunoglobulins A, G and M, and reduced IL-6 levels (P < 0.05).It also enhanced caecal amylase, carboxymethyl cellulase, and trypsin activities, restored villus height, mucosal thickness, villus/crypt ratio (P < 0.05), and increased the expression of tight-junction and metabolic genes while downregulating proinflammatoryrelated genes (P < 0.05).Moreover, Lactobacillus CNCM I-4622 significantly increased caecal microbial α-diversity and improved microbial community structure and functional pathways (P < 0.05).Dietary supplementation with Lactobacillus CNCM I-4622 effectively alleviated Salmonella-induced caecal damage, suppressed inflammation, improved digestive function, and stabilised microbial homeostasis in Haidong chickens.These results support Lactobacillus CNCM I-4622 as a promising alternative to antibiotics for maintaining poultry health under pathogenic stress.