Implementation of Three Gallium-Based Complexes in the "Trojan Horse" Antibacterial Strategy against A. baumannii : A DFT Approach.

Microorganisms of the ESKAPE group pose an enormous threat to human well-being, thus requiring a multidisciplinary approach for discovering novel drugs that are not only effective but utilize an innovative mechanism of action in order to decrease fast developing resistance. A promising but still hardly explored implementation in the "Trojan horse" antibacterial strategy has been recognized in gallium, an iron mimicry species with no known function but exerting a bacteriostatic/bactericidal effect against some representatives of the group. The study herewith focuses on the bacterium A. baumannii and its siderophore acinetobactin in its two isomeric forms depending on the acidity of the medium. By applying the powerful tools of the DFT approach, we aim to delineate those physicochemical characteristics that are of great importance for potentiating gallium's ability to compete with the native ferric cation for binding acinetobactin such as pH, solvent exposure (dielectric constant of the environment), different metal/siderophore ratios, and complex composition. Hence, the provided results not only furnish some explanation of the positive effect of three Ga 3+ -based anti-infectives in terms of metal cation competition but also shed light on reported in vitro and in vivo observations at a molecular level in regard to gallium's antibacterial effect against A. baumannii .