Epitope mapping of Salmonella flagellar hook-associated protein, FlgK, with mass spectrometry-based immuno-capture proteomics using chicken (Gallus gallus domesticus) sera

Salmonella, a Gram-negative rod, is the leading foodborne pathogen associated with human acute bacterial gastroenteritis worldwide. The Salmonella flagellum is responsible for bacterial movement, colonization and invasion in the host gastrointestinal tract. The flagellum has a complex structure, composed of more than 35 proteins. Among them, we were interested in the flagellar hook-associated protein (FlgK), which is an immunodominant protein in chickens. In this communication, we applied mass spectrometry-based proteomics in conjunction with chicken immunized sera to map the linear immunoepitopes in the FlgK protein, validated the epitopes with peptide ELISA, and determined serum reactivity to the epitopes from commercial chickens. We previously demonstrated the FlgK proteins are highly conserved among Salmonella serovars. The rFlgK protein was produced by the recombinant technique, and was able to induce immune response in chickens. Further, this study identified four peptides (AEG, GAQ, TAD and LEI) in the rFlgK protein that were captured by sera from chickens immunized with the rFlgK protein. These four peptides were also reacted to 64 individual serum samples collected from 44 − 52 weeks old chickens, suggesting that these peptides may represent the shared immuno-epitopes on the FlgK protein. The findings of the specific shared linear immuno-epitopes on the FlgK protein in this study provide a rationale for further evaluation to determine their utility as epitope vaccines covering multiple serotypes for chicken immunization, and subsequently, for providing safer poultry products for human consumption.