Intranasal immunization with recombinant Omp34 and its derivative engineered construct, rOmp34L3×5, against Acinetobacter baumannii pulmonary infection

The emergence of extreme and pan-drug-resistant strains of Acinetobacter baumannii has intensified the need for effective prevention strategies, including developing vaccines. This study evaluates the immunogenicity and protective efficacy of the outer membrane protein Omp34 and its engineered construct, rOmp34L3×5, as potential vaccine candidates against A. baumannii pulmonary infections. The recombinant proteins were expressed and purified using Ni-NTA columns. The clinical colistin-resistant strain of A. baumannii Ab/TU/ColR was used in the murine pneumonia challenge experiments. Mice were immunized intranasally with the recombinant proteins. IgG, IgA titers, and their reactivity were assessed. Bacterial challenges and survival analysis were performed. Post-challenge, bacterial burdens in organs and histopathology of the lungs were evaluated. The results demonstrated that both vaccine candidates elicited strong immune responses, particularly with significant IgA and IgG antibody production. However, immunization with rOmp34L3×5 showed relatively stable IgG levels over 22 weeks, whereas rOmp34 alone induced higher IgG titers. Lung, spleen, and liver cultures confirmed the effectiveness of the specific antibodies in clearing bacterial loads, with histological analysis revealing normal lung tissue in immunized mice, contrasting with severe inflammation in controls. These findings suggest that rOmp34 and rOmp34L3×5 have the potential to serve as effective immunogens in preventing A. baumannii infections. Nonetheless, the variability in immune response depending on the clinical strain underscores the need for further studies to optimize vaccine efficacy across diverse A. baumannii isolates. • Intranasal rOmp34 & rOmp34L3×5 protect against A. baumannii • Both immunogens induce strong systemic and mucosal antibody responses • rOmp34 elicits higher IgG; rOmp34L3×5 shows stable IgA over time • Immunization significantly reduces bacterial burden in lungs, spleen, and liver • rOmp34L3×5 provides broader protection despite lower IgG titers