Bacillus velezensis alleviates PM2.5-induced intestinal injury and dysbiosis in broilers via the “lung-gut axis”

This study investigated how tracheal instillation of Bacillus velezensis mitigates PM 2.5 -induced lung injury and counteracts its adverse effects on distal intestinal health in broilers via the “lung-gut axis”. Five groups were randomly selected from among seventy-five 14-day-old AA broilers: Control, Saline, PM2.5, B. velezensis , and B. velezensis + PM2.5. Results showed that compared with the Saline group, PM 2.5 exposure disrupted lung structure and significantly upregulated TLR4 , MyD88 , NF-κB , IL-18 , and IFN-γ related inflammatory factors via the TLR4/MyD88/NF-κB signaling axis ( P < 0.05). In addition, it significantly reduced jejunal villus height through the action of the “lung-gut axis” ( P < 0.05), decreased the levels of IL-10 , Claudin-1 , and Occludin while increasing that of IL-22 ( P < 0.05). Analysis of the cecal microbiota found that PM 2.5 reduced the Shannon index of bacterial communities and raised the relative abundance of Bacteroidota , Pseudomonadota , and Flavonifractor . Co-treatment with B. velezensis + PM 2.5 reversed the above changes, significantly improved lung and intestinal morphology, enhanced jejunal barrier function, reduced lung and jejunal inflammatory responses, and increased the relative abundance of Faecalibacterium . Based on KEGG functional prediction, the PM 2.5 group was enriched in microbial metabolic pathways, such as two-component systems and ABC transporters. Tracheal instillation of B. velezensis can improve the expression of genes associated with lung injury via the TLR4/MyD88/NF-κB signaling axis and effectively alleviate PM 2.5 -induced distal jejunal damage, barrier dysfunction, inflammatory response, and dysbiosis by mediating the “lung-gut axis”. This could provide a theoretical support and scientific basis for seeking probiotics to improve PM 2.5 harm.