Wildlife-derived Lactobacillus agilis LA-V4 alleviates Salmonella Typhimurium infection in broilers through gut microbiota remodeling and hepatic autophagy restoration.

Salmonella Typhimurium (S. Typhimurium) is a major enteric pathogen in poultry production, causing substantial economic losses and posing a serious public health threat through the contamination of animal-derived food products. Although probiotics are increasingly recognized as promising alternatives to antibiotics for controlling Salmonella infection, their mechanistic basis of protection remains insufficiently defined. Here, we evaluated the probiotic efficacy of Lactobacillus agilis LA-V4, a stress-tolerant strain isolated from vulture feces, in healthy Arbor Acres broilers and in a prophylactic model of S. Typhimurium infection. In healthy birds, LA-V4 supplementation enhanced mucosal immune responses and appeared to alleviate hepatic metabolic stress associated with rapid early growth. In S. Typhimurium-challenged broilers, LA-V4 markedly improved intestinal barrier integrity by upregulating the tight junction proteins ZO-1 and Occludin. Moreover, LA-V4 pretreatment was associated with a significantly lower relative abundance of Salmonella-assigned sequences in the cecal microbiota and partially ameliorated infection-associated microbial dysbiosis, as evidenced by decreased relative abundances of Firmicutes-related taxa, such as Lachnospiraceae and Erysipelotrichales, together with increased relative abundances of Lactobacillus and several putative short-chain fatty acid-producing taxa, including v9d2013_group, Phascolarctobacterium, and Fournierella. In hepatic tissue, LA-V4 restored autophagic activity, as reflected by increased LC3-II and Beclin1 expression and reduced p62 accumulation. Taken together, our findings identify L. agilis LA-V4 as a novel probiotic candidate that protects broilers against S. Typhimurium infection through coordinated regulation of the gut microbiota, intestinal barrier function, and hepatic autophagic responses.