Identification and protective efficacy characterization of novel immunogenic antigens for Salmonella Enteritidis vaccines

The global poultry industry incurs substantial economic losses due to Salmonella enterica serovar Enteritidis (S. Enteritidis), underscoring the urgent need for cross-protective vaccines capable of addressing evolving pathogen diversity. Using an integrative vaccinology approach, we systematically screened immunoreactive proteins to identify novel subunit vaccine candidates. Eight candidate proteins, including type III secretion system components (SipA, SopE2, SipB, SipC), membrane-associated proteins (TolA, TolC, LamB), and the virulence factor MipA, demonstrated pronounced antigenic and immunogenic properties. Further investigation revealed that SipC and TolC induced balanced Th1/Th2 responses and IL-17A secretion, contributing to multifaceted immunity. Opsonophagocytic assays demonstrated that antisera against SipC and TolC significantly enhanced neutrophil-mediated killing of homologous and heterologous strains. Notably, antisera against SipC exhibited enhanced efficacy in promoting neutrophil killing of the heterologous UK-1 strain. In challenge studies, SipC provided 66.7 % protection against a homologous strain and demonstrated 50 % cross-protection against the UK-1 strain, thereby exhibiting superior efficacy compared to other candidate antigens. Both antigens significantly decreased bacterial loads in visceral organs following challenge. This study identifies SipC, and to a lesser degree TolC, as potential broad-spectrum subunit vaccine antigens, providing a foundation for next-generation poultry salmonellosis vaccines with extensive protective efficacy.