Immunization of chicken with flagellin adjuvanted Salmonella enteritidis bacterial ghosts confers complete protection against chicken salmonellosis

The present study describes the generation of Salmonella enteritidis (SE) ghosts with a surface decorated Salmonella Typhimurium (ST) flagellin (FliC) antigen for immune enhancement and strain-specific protection. The ghosts were generated by biological means using pJHL184::fliC temperature inducible plasmid where the lysis occurs by phage PhiX174 lysis gene E expression. Being an inactivated strain, no environmental contamination was observed by fecal shedding upon inoculation into the chicken. To test the protective immune responses, ghost vaccination was conducted via the intramuscular route using chicken as the model organism. The development of antigen-specific humoral, cell-mediated, and protective immune responses was assessed. Compared to vector alone and phosphate-buffered saline (PBS) control groups, pJHL184::fliC ghost could generate significantly high antigen-specific IgY and cell-mediated immune (CMI) responses measured by a peripheral blood mononuclear cell proliferation, flow cytometer, and cytokine responses elicited by stimulated splenic T-cells (P < 0.05). The adjuvant effect induced by FliC was demonstrated by elicitation of Toll-like receptor 5 (TLR5). To test the protection efficacy, chickens were challenged with both SE and ST wild type (WT) strains, and the protection efficacy was assessed by determining the presence of challenging strains in the spleen and liver, and by assessing the histopathological alterations. Complete clearance of the challenged strain and least inflammatory signs were evident in the SE ghosts vaccinated group compared to the vector and PBS control. The elimination of both SE and ST in chicken organs ensures the intramuscular immunization of the present SE ghost vaccine can reduce SE and ST contamination levels in chicken that can be beneficial to prevent enteric infections in humans.