Abstract
In this study, we incorporated deletion of the O-antigen ligase gene to an attenuated Salmonella Enteritidis (SE) strain, JOL919 (SE PS; Δlon ΔcpxR), using the Lambda-Red recombination method and evaluated the safety and immunological aspects of the novel genotype, JOL2381 (SE VS: Δlon, ΔcpxR, ΔrfaL). Assessment of fecal shedding and organ persistence following administration via oral and IM routes revealed that the SE VS was safer than its parent strain, SE PS. Immunological assays confirmed that immunization via the oral route with SE PS was superior to the SE VS. However, chickens immunized with SE PS and SE VS strains via the IM route showed higher humoral and cell-mediated immune responses. Compared to PBS control, the IM route of immunization with SE VS resulted in a higher IgY antibody titer and expansion of CD4(+) and CD8(+) T-cell populations, which resulted in the clearance of Salmonella from the liver and splenic tissues. Furthermore, deletion of the O-antigen ligase gene caused lower production of LPS-specific antibodies in the host, promoting DIVA functionality and making it a plausible candidate for field utilization. Due to significant protection, high attenuation, and environmental safety concerns, the present SE VS strain is an ideal choice to prevent chicken salmonellosis and ensure public health.