Effects of Salmonella Enteritidis infection on TLRs gene expression and microbial diversity in cecum of laying hens

Salmonella Enteritidis (SE) is an important foodborne pathogen primarily causing human disease through contaminated food and water. In the current study, to assess the effect of Salmonella Enteritidis infection on the immune system and the microbial diversity of cecum and oviduct in chickens, twelve 24-week-old SE-negative White Leghorn layers were randomly selected and divided into 2 groups. Chickens in the challenge group were orally inoculated with SE, and chickens in the control group received an equal amount of sterilized Phosphate Buffered Saline solution. Serum and tissue samples (cecum, oviduct, ovary, liver, spleen, and pancreas) were collected at 7 days and 14 days post-infection (dpi). Quantitative PCR was used to detect the expression of Toll-like receptors (TLRs) in the cecum, oviduct and ovary. To understand the influence of SE infection on the microbial profile of the cecum and oviduct, microbial community composition of the cecal contents and oviducal contents were analyzed through 16S rRNA sequencing. Results showed that SE infection caused damage to the digestive organs, reproductive organs, and immune organs in laying hens. The expression of TLR1a, TLR1b, TLR2, TLR4, TLR5, TLR7 and TLR15 in the cecum were induced, and the content of IFN-γ, TNF-α, IL-2 and IL-18 in serum increased after SE infection. The composition of the microbial community significantly changed in cecal content, the dominant phylum of Firmicutes increased, and Bacteroidetes decreased significantly. In the oviduct, the microbial diversity became complicated, the dominant bacteria Faecalibacterium was significantly increased, and Bacteroides was significantly decreased. This study investigated the effects of SE infection in laying hens, including host innate immunity, the expression of TLRs, and changes in the composition of microbes in the cecum and reproductive tract. Our results may provide a scientific basis for the Salmonella Enteritidis control in chicken, the maintenance of oviduct function, and the guarantee of clean egg production.