Screening of lipid-A related genes and development of low-endotoxicity live-attenuated Salmonella gallinarum by arnT deletion that elicits immune responses and protection against fowl typhoid in chickens

In the present study, lipid-A gene mutants of Salmonella gallinarum (SG) were screened, and the arnT mutant exhibited optimal acidic and oxidative-stress and macrophage-survival. Modifying lipid-A by arnT-deletion resulted in significantly reduced endotoxicity, virulence, and mortality. Therefore, the arnT-deleted vaccinecandidate strain JOL2841 was constructed and demonstrated to be safe due to appropriate clearance by the chicken immune system. The reduced-endotoxicity of JOL2841 was evident from the downregulation of TNF alpha and IL-1 beta inflammatory cytokines, no inflammatory signs in organ gross-examination, and histopathological analysis. The IgY and IgA antibody titres, CD4, and CD8 T-cell population improvements, and IL-4, IL-2, and INF gamma expression decipher the profound Th2 and Th1 immunogenicity. Consequently, JOL2841 exhibited prominent protection against wild-type SG challenge, as revealed by organ pathogen-load determination, organ grossexamination, and histopathological examination. Overall, the study represented the first report of arnT deficient SG resulted in negligible endotoxicity, low-virulence, safety and coordinated elicitation of humoral and cell-mediated immune response in chickens.

Automated summary

In this study, lipid-A gene mutants of Salmonella gallinarum were screened and the arnT mutant showed optimal adaptation to acidic and oxidative stress as well as macrophage survival. Deleting the arnT gene resulted in reduced endotoxicity, virulence, and mortality. A safe vaccine candidate strain, JOL2841, with arnT deletion was constructed and demonstrated to be cleared by the chicken immune system. JOL2841 showed reduced endotoxicity, improved immune response, and provided protection against wild-type SG challenge in chickens.