Protective potentials of a siderophore receptor against Acinetobacter baumannii infections

Acinetobacter baumannii causes nosocomial infections and high mortality rates in the world. Since antibiotic treatment is complicated by extensive drug resistance in A. baumannii strains, other approaches such as vaccination can be a cost-effective solution. Siderophore receptor related to cluster 1 of iron uptake system (WP_000413999) is expressed in early stages of A. baumannii's infection under iron restricted conditions. In this study, structural characterization and immunogenicity of the target protein in a murine sepsis model were assessed. Structural properties of the siderophore receptor were determined by bioinformatics tools. The gene encoding the antigen was cloned in E. coli BL21(DE3) and was then expressed. The purified recombinant protein was administered to the mice subcutaneously for antibody production. The immunized mice were challenged with the A. baumannii at lethal dose via intraperitoneal injection. Blast results revealed more than 97% identity of the protein in 3472 strains of A. baumannii. This receptor is a TonB-dependent transporter with a barrel domain composed of 22 beta-strands connected by external loops and periplasmic turns. Experimental findings showed that the recombinant protein had no toxicity effect on A549 cells. Moreover, the studied protein was able to induce a specific antibody response in the mice. Survival rate of the passive immunized mice was improved against sepsis caused by A. baumannii ATCC 19606 and ABI022 clinical isolate. The study indicated that this siderophore receptor can be considered for further analysis as a potential vaccine target against A. baumannii.