In Silico Analyses of Extracellular Proteins of Acinetobacter baumannii as Immunogenic Candidates

Background: Acinetobacter baumannii is an important nosocomial pathogen causing high morbidity and mortality in immunocompromised patients with prolonged hospitalization. Multidrug-resistant A. baumannii infections are on the rise worldwide. Therefore, the discovery of an effective vaccine against this bacterium seems necessary as a cost-effective and preventive strategy. Methods: In this present study, 35 genomes of A. baumannii strains were considered, and the extracellular proteins were selected, maximally having one transmembrane helix with high adhesion probability and no similarity to host proteins, as immunogenic candidates using the web tool Vaxign. Subsequently, the role of these selected proteins in bacterial pathogenesis was investigated using VICMpred. Then, the major histocompatibility complex class II, linear B-cell epitopes, and conservation of epitopes were identified using the Immune Epitope Database, BepiPred, and Epitope Conservancy Analysis, respectively. Finally, the B-cell discontinuous epitopes of each protein were predicted using ElliPro and plotted on the three-dimensional structure (3D) of the proteins. The role of the unknown proteins was predicted using the STRING database. Results: In this study, eight acceptable immunogenic candidates, including FilF, FimA, putative acid phosphatase, putative exported protein, subtilisin-like serine protease, and three uncharacterized proteins, were identified in A. baumannii. Conclusions: The results of the STRING database showed that these three uncharacterized proteins play a role in nutrition (heme utilization), peptide bond cleavage (serine peptidases), and cellular processes (MlaD protein). Extracellular proteins might play a catalyst role in the outer membrane protein-based vaccine of A. baumannii. Furthermore, this study proposed a list of potent immunogenic candidates of extracellular proteins.