Evaluation of recombinant Salmonella expressing the flagellar protein fliC for persistence and enhanced antibody response in commercial turkeys

Salmonella enterica serovar Enteritidis (SE) is one of the most common causes of human foodborne illness in the United States. Previous research indicates that antibodies against the fliC protein can provide protection against Salmonella challenge in mice. To generate a vaccine that effectively protects poultry against multiple Salmonella serotypes, novel attenuated strains of SE were developed to express a fliC peptide sequence on the outer membrane protein lamB in association with an M2e (marker) epitope. In 3 separate trials, poults were immunized with 10(7) to 10(8) cfu/poult of the appropriate recombinant Salmonella strains (ΔSE-M2e or ΔSE-M2e-fliC) via oral gavage on the day of hatch and again on d 21 posthatch. Liver, spleen, and cecal tonsils were aseptically removed on d 7, 14, 21, 28, 35, and 42 posthatch for detection of Salmonella, and blood samples were obtained at these same time points for determination of an M2e-specific antibody response. In all 3 trials, the ΔSE-M2e-fliC strain exhibited significantly less invasion of the liver and spleen at d 7 and 14 when compared with ΔSE-M2e or SE phage type 13A (P < 0.05). Similarly, colonization of the cecal tonsils was decreased in the poults immunized with the ΔSE-M2e-fliC strain. By d 21, the ΔSE-M2e-fliC strain exhibited a significantly higher M2e-specific antibody response when compared with the negative control and SE phage type 13A groups (P < 0.05). However, no significant differences in M2e-specific antibody responses were observed between the ΔSE candidate vaccine strains throughout the study. Overall, these data suggest that oral live attenuated Salmonella-vectored vaccines expressing a fliC peptide sequence are able to elicit a humoral immune response in commercial poults and may contribute to a reduction in Salmonella organ invasion and colonization.