Differential cytokine profiling and microbial species involved in cecal microbiota modulations in SPF chicks immunized with a dual vaccine against Salmonella Typhimurium infection

Salmonella Typhimurium (ST) infection in laying hens is a significant threat to public health and food safety. Host resistance against enteric pathogen inva-sion primarily relies on immunity and gut barrier integrity. This study applied the ST infection model and a dual live vaccine containing Salmonella Enteritidis (SE) strain Sm24/Rif12/Ssq and ST strain Nal2/Rif9/Rtt to investi-gate the cellular cytokine expression profiles and the differ-ential community structure in the cecal microbiota of specific-pathogen-free (SPF) chicks and field-raised layers. The results showed that ST challenge significantly upregulated expressions of IL-1/3 in SPF chicks. Vaccina-tion, on the other hand, led to an elevation in IFNg expres-sion and restrained IL-1/3 levels. In the group where vaccination preceded the ST challenge (S.STvc), height-ened expressions of IL-1/3, IL-6, IL-10, and IL-12/3 were observed, indicating active involvement of both humoral and cell-mediated immunity in the defense against ST. Regarding the cecal microbiota, the vaccine did not affect alpha diversity nor induce a significant shift in the micro-bial community. Conversely, ST infection significantly affected the alpha and beta diversity in the cecal micro -biota, reducing beneficial commensal genera, such as Blau-tia and Subdoligranulum. MetagenomeSeq analysis reveals a significant increase in the relative abundance of Faecali-bacterium prausnitzii in the groups (S.STvc and STvc) exhibiting protection against ST infection. LEfSe further demonstrated Faecalibacterium prausnitzii as the promi-nent biomarker within the cecal microbiota of SPF chicks and field layers demonstrating protection. Another bio-marker identified in the S.STvc group, Eubacterium cop-rostanoligenes, displayed an antagonistic relationship with Faecalibacterium prausnitzii, suggesting the limited biological significance of the former in reducing cloacal shedding and tissue invasion. In conclusion, the applica-tion of AviPro Salmonella DUO vaccine stimulates host immunity and modulates cecal microbiota to defend against ST infection. Among the microbial modulations observed in SPF chicks and field layers with protection, Faecalibacterium prausnitzii emerges as a significant spe-cies in the ceca. Further research is warranted to elucidate its role in protecting layers against ST infection.