Evaluation of recombinant Salmonella expressing CD154 for persistence and enhanced antibody response in commercial turkeys

Foodborne illness due to Salmonella is a worldwide public health concern and epidemiological evidence has identified poultry and poultry products as a significant source of human Salmonella infection. To discover an effective vaccine that protects poultry against multiple Salmonella serotypes, several novel attenuated Salmonella Enteritidis strains (DeltaSE) were developed to express variations of a potential immune-enhancing CD154 peptide sequence on the outer membrane protein lamB in association with a M2e (marker) epitope. The 3 CD154 peptide sequences evaluated in this study correspond to those naturally occurring in turkeys, humans, and chickens. In 3 separate trials, poults were immunized with 10(7) to 10(8) cfu/poult of the appropriate recombinant Salmonella strains (DeltaSE-M2e, DeltaSE-M2e-T/CD154, DeltaSE-M2e-H/CD154, DeltaSE-M2e-C/CD154) via oral gavage on day of hatch and again on 21 d 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, DeltaSE strains exhibited significantly less invasion of the liver and spleen at d 7 when compared with Salmonella Enteritidis phage type 13A (P < 0.05). In 2 of the 3 trials, the DeltaSE strains expressing a CD154 peptide sequence further decreased invasion of the liver and spleen. Similarly, colonization of the cecal tonsils was also decreased in the poults immunized with the DeltaSE strains. However, there were no differences in colonization or invasion due to the amino acid sequence of the CD154 insert in all 3 trials. By d 21, the DeltaSE strains exhibited a significantly higher M2e-specific antibody response when compared with the negative control and SE13A groups (P < 0.05). However, no significant differences in M2e-specific antibody responses were observed between any of the DeltaSE candidate vaccine strains expressing CD154 throughout the study. Overall, these data suggest that oral live attenuated Salmonella-vectored vaccines expressing a foreign 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.