Lipophilic Ga Complex with Broad-Spectrum Antimicrobial Activity and the Ability to Overcome Gallium Resistance in both Pseudomonas aeruginosa and Staphylococcus aureus

Antibiotic resistance (AR) necessitates the discovery of new antimicrobials with alternative mechanisms of action to those employed by conventional antibiotics. One such strategy utilizes Ga3+ to target iron metabolism, a critical process for survival. Still, Ga-based therapies are generally ineffective against Gram-positive bacteria and promote Ga resistance. In response to these drawbacks, we report a lipophilic Ga complex, [Ga2L3(bpy)2] (L = 2,2′-bis(3-hydroxy-1,4-naphthoquinone; bpy = 2,2′-bipyridine)), effective against drug-resistant Pseudomonas aeruginosa (DRPA; minimum inhibitory concentration, MIC = 10 μM = 14.8 μg/mL) and methicillin-resistant Staphylococcus aureus (MRSA, MIC = 100 μM = 148 μg/mL) without iron-limited conditions. Importantly, [Ga2L3(bpy)2] shows noticeably delayed and decreased resistance in both MRSA and DRPA, with only 8× MIC in DRPA and none in MRSA after 30 passages. This is likely due to the dual mode of action afforded by Ga (disruption of iron metabolism) and the ligand (reactive oxygen species production). Overall, [Ga2L3(bpy)2] demonstrates the utility of lipophilic metal complexes with multiple modes of action in combatting AR in Gram-positive and Gram-negative bacteria.