The extradomain a of fibronectin enhances the efficacy of lipopolysaccharide defective Salmonella bacterins as vaccines in mice

The Extradomain A from fibronectin (EDA) has an immunomodulatory role as fusion protein with viral and tumor antigens, but its effect when administered with bacteria has not been assessed. Here, we investigated the adjuvant effect of EDA in mice immunizations against Salmonella enterica subspecies enterica serovar Enteritidis (Salmonella Enteritidis). Since lipopolysaccharide (LPS) is a major virulence factor and the LPS O-polysaccharide (O-PS) is the immunodominant antigen in serological diagnostic tests, Salmonella mutants lacking O-PS (rough mutants) represent an interesting approach for developing new vaccines and diagnostic tests to differentiate infected and vaccinated animals (DIVA tests). Here, antigenic preparations (hot-saline extracts and formalin-inactivated bacterins) from two Salmonella Enteritidis rough mutants, carrying either intact (SEΔwaaL) or deep-defective (SEΔgal) LPS-Core, were used in combination with EDA. Biotinylated bacterins, in particular SEΔwaaL bacterin, decorated with EDAvidin (EDA and streptavidin fusion protein) improved the protection conferred by hot-saline or bacterins alone and prevented significantly the virulent infection at least to the levels of live attenuated rough mutants. These findings demonstrate the adjuvant effect of EDAvidin when administered with biotinylated bacterins from Salmonella Enteritidis lacking O-PS and the usefulness of BEDA-SEΔwaaL as non-live vaccine in the mouse model.