Investigating Immunogenicity and Protectivity of Subcutaneous Administration of Salmonella Dublin Bacterin in Mice

Background: Given the significant zoonotic threat posed by Salmonella enterica serovar Dublin (S. Dublin) and its substantial impact on animal populations and public health, the objective of the present study was to assess the immunogenicity and protectivity of subcutaneous administration of Salmonella Dublin bacterin in a murine model. 
Materials and Methods: Specific pathogen-free female BALB/c mice were tested for Salmonella-free status, and housed in controlled conditions. A formalin-killed bacterin was prepared from a local isolate of S. Dublin using a well-established protocol, ensuring bacterial inactivation and safety. Groups 1 through 3 of mice were received, respectively, either phosphate buffered saline plus alum or a single dose of inactivated bacterins with and without alum adjuvant via subcutaneous route. Immune responses were evaluated through microagglutination, enzyme-linked immunosorbent assay, delayed-type hypersensitivity, interferon-gamma assays, and challenge with viable S. Dublin.
Results: Microagglutination and enzyme-linked immunosorbent assay tests revealed alum-adjuvanted injection as the best method for stimulation of anti-S. Dublin antibodies production. The gamma interferon production and delayed hypersensitivity tests, crucial for cellular immunity, were also most elevated in mice injected with alum-adjuvanted S. Dublin bacterin. After the challenge with the live bacteria, the isolation rate of S. Dublin was significantly different (P=0.03) among the different groups but only mice injected with alum-adjuvanted showed a significant difference (P≤0.05) compared to the control group.
Conclusion: This study emphasizes the efficacy of alum as an adjuvant in inactivated S. Dublin vaccines. Insights gained from both humoral and cellular immune responses, provide valuable knowledge for the development of S. Dublin vaccination strategies.