Immunogenicity of conserved cork and β-barrel domains of baumannii acinetobactin utilization protein in an animal model.

Abstract

The uptake of the ferric-acinetobactin complex into the periplasmic space relies on the baumannii acinetobactin utilization (BauA) protein. BauA is composed of cork and the β-barrel domains. We constructed a recombinant protein from conserved antigenic domains of cork and the β-barrel of BauA to evaluate their immunogenic role in an animal model. The selected bauA domains were amplified from a purified genome of Acinetobacter baumannii ATCC 19606. The domains were then cloned into pET28a and the proteins expressed in E. coli BL21 (DE3) were purified using nickel nitrilotriacetic acid chromatography. Mice and rabbits were immunized with an intraperitoneal injection of the recombinant BauA (rBauA). The highest immune response was achieved after the third booster injection while hyperimmunity was achieved after the second booster injection in rabbits. Immunized mice challenged with live A. baumannii survived, whereas all unimmunized mice in the control group died after 24 h. Mice injected with 10(9) colony forming units of A. baumannii preincubated with pure immune rabbit sera survived. Bacterial cultures from mice spleen and liver specimens revealed the absence of bacterial growth in the immunized groups. The rBauA could be used as a prophylactic agent and further tests should be carried out to see if it may be useful in a clinical setting against A. baumannii infections.