Immunogenicity of the combination of periplasmic proteins BauA, Oma87, and Bap from Acinetobacter baumannii in a murine sepsis model

Background and Objective: Acinetobacter baumannii is a serious challenge to the healthcare system as a multi-drug-resistant bacterium. BauA is a siderophore of A. baumannii. Oma87 has been stated as an immunogenic outer membrane protein per reverse vaccinology. Biofilm-associated protein (Bap) plays an indispensable role in biofilm formation by this pathogen and makes it resistant to a wide range of antibiotics and lethal conditions. The persistence and colonization of A. baumannii can be prevented by raising antibodies against BauA, Oma87, and Bap. Materials and Methods: The recombinant proteins BauA, Oma87, and Bap were expressed and purified and injected subcutaneously in single and/or in combination forms to BALB/c mice and then they were challenged intraperitoneally with a lethal dose of 50% A. baumannii ATCC19606. The serum of combined mice was injected intravenously through the tail vein to create passive immunity in non-immune healthy mice. The mice’s spleen, liver, and lung tissues were examined to check the bacterial load. Results: Oma87 and Bap in combination with BauA in the mouse model brought about significant immunity. Antibodies produced in mice successfully detected and bound the combination of antigens in the mouse model. After immunizing and challenging mice with Acinetobacter baumannii ATCC19606 admixed with mucin 100%, the survival rate was monitored. Passive immunization using the sera of mice immunized against Oma87 and BauA as well as BauA and Bap yielded 85.7% survival. Conclusion: The combination of BauA with Oma87 and Bap brought about higher protectivity against A. baumannii infection than their individual administration.