Homologous prime-boost immunization with live attenuated Salmonella enterica serovar Senftenberg and its preventive efficacy against experimental challenge with various strains of S. Senftenberg

Background: The heterogeneity observed regarding persistence, and subsequent fecal shedding pattern of the Salmonella Senftenberg (S. Senftenberg) serovar in chicken's calls for development of the optimized immunization strategy which can provide protection against various S. Senftenberg isolated. Optimization of an immunization strategy with a live attenuated S. Senftenberg (∆lon and ∆cpxR) vaccine candidate (JOL1587) was undertaken in this study to evaluate the ability of a homologous prime-boost immunization strategy (using JOL1587) to confer protection against four different S. Senftenberg isolates in chickens. Results: After oral immunization with JOL1587, the humoral, mucosal and cell-mediated immune responses were significantly higher in double immunized chickens than in single immunized and control group chickens. A significant increase in the multifunctional cytokine IL-6 and in helper and cytotoxic T cell populations after a booster immunization also indicated the advantage of double over single immunization. The four different S. Senftenberg field isolates were characterized by their persistence levels in chickens, and were subsequently used for challenge experiments to evaluate the differences in protective efficacy conferred by single and double immunization. Chickens from the doubleimmunized group exhibited significant reduction in the shedding of all four wild-type S. Senftenberg challenge strains below the detection limit in the fecal samples. Single immunized chickens showed a decrease in fecal shedding, but failed to exhibit complete protection against all the challenge strains. Conclusion: Although single immunization with JOL1587 showed a reduction in the fecal shedding of challenge strains, only the homologous prime-boost immunization strategy provided an adequate immune response for increased protection against all four challenge strains of S. Senftenberg from the feces of chickens.