Acinetobacter baumannii is a highly pathogenic, multidrug-resistant bacterium, posing a significant clinical challenge. Targeting key proteins such as OmpA and LigA offers potential for novel antimicrobial strategies. In this study, we evaluated the antimicrobial activity of Origanum vulgare essential oil against A.
baumannii strains and investigated the mechanism by which the main components (carvacrol, beta-caryophyllene, gamma-terpinene, thymol, and p-cymene) in the supplement have an antimicrobial effect on A. baumannii using computational techniques. Amino acid sequences for OmpA and LigA were obtained from NCBI and modeled in 3D using Swiss-Model, AlphaFold, and GalaxyWeb.
Ligands were sourced from PubChem, and models were evaluated with PROCHECK and ERRAT, while active binding sites were identified through Consurf analysis. Protein-ligand docking was performed using HDOCK and AutoDock Vina, with interactions analyzed via the PLIP tool. The MIC values for Origanum vulgare were determined following CLSI guidelines, using emulsified oils and bacterial inocula in 96-well plates, incubated at 37°C for 24 hours, with MIC defined as the lowest concentration showing no growth, measured at 450 nm absorbance.
For OmpA, HDOCK identified thymol (-95.53) and carvacrol (-93.58) as the top-scoring ligands, whereas AutoDock Vina highlighted γ-terpinene (-5.6) and p-cymene (-5.4). For LigA, carvacrol (-112.21) and thymol (-111.73) showed the strongest HDOCK binding, while AutoDock Vina favored p-cymene (-7.0) and carvacrol (-6.9).
The lowest MIC against the A13 strain was observed with a 1/64 dilution of Origanum vulgare oil, while 1/16 and 1/32 dilutions inhibited other strains. These results support the potential of these essential oils as antimicrobial agents.