The identification of two protective DNA vaccines from a panel of five plasmid constructs encoding Brucella melitensis 16M genes.

Five candidate genes from the Brucella melitensis 16M genome were selected. Eukaryotic expression plasmids encoding these antigens were constructed and expression was verified in vitro from transfected Cos7 cells. Each vaccine was assessed for protective efficacy in a BALB/c mouse brucellosis infection model. From these experiments two protective DNA vaccines were identified: p-omp25 and p-ialB. The Omp25 antigen (BMEI1249) has previously been studied in terms of Brucella virulence, serodiagnosis and as a protective antigen. However, this study represents the first report of a significant protective effect achieved against B. melitensis 16M challenge using the Omp25 antigen in a DNA vaccine approach. The other protective vaccine identified in this study was p-ialB. The ialB candidate (BMEI1584) was selected based upon its' putative function as an invasion protein which was assigned due to shared identity with the invasion protein B (ialB) of Bartonella bacilliformis. This candidate has not previously been investigated with regard to Brucella virulence or pathogenesis. This study is the first report to identify the Brucella invasion protein B (BMEI1584) as a novel protective antigen for brucellosis.