Comparative analysis of the oral and injectable form of heat-inactivated Salmonella Enteritidis vaccine efficacy in commercial chickens
Abstract
Salmonella enterica subsp. enterica serovar Enteritidis (Salmonella Enteritidis) is a non-typhoidal Salmonella (NTS), a facultatively anaerobic, Gram-negative bacteria commonly residing in the intestines of chickens, cattle, rodents, reptiles, and amphibians. Specifically, Salmonella Enteritidis causes salmonellosis in chickens, characterised by weakness, reduced appetite, stunted growth, and diarrhoea. Although both live and inactivated vaccines are currently used in poultry, they present several drawbacks. While live vaccines generally are more effective at stimulating strong immune responses, they carry the risk of reverting to virulence. In contrast, inactivated or killed vaccines are safer but often elicit weaker immune responses, requiring multiple booster doses and adjuvants to achieve protective immunity. These limitations highlight the need for improved vaccine strategies that are both safe and highly immunogenic. To develop a safer and more practical vaccine strategy against salmonellosis in commercial chickens, we evaluated the immunogenicity and protective efficacy of a heat-inactivated whole-cell S. Enteritidis (SE) vaccine. Two routes of vaccine administration were chosen, oral and injectable, to compare their efficacy using a prime-boost regimen. We demonstrated that oral administration of the heat-inactivated vaccine elicited stronger mucosal antibody responses than the injectable route. Moreover, orally vaccinated birds were significantly protected against challenge infection without adverse effect on gut health. These findings indicate that the mucosal (oral) delivery of heat-inactivated S. Enteritidis vaccine can represent a promising and safe approach for developing an effective vaccine against salmonellosis in commercial chickens.