Copper(II) carboxylate complexes inhibit Staphylococcus aureus biofilm formation by targeting extracellular proteins

Three copper(II) complexes of diphenyl acetic acid (DPAA) pyridine (py), 2,2΄-dipyridylamine (dpa), and 4,7-diphenyl, 1,10-phenanthroline (di-phen), [Cu₂(DPAA)₄(py)₂] (Cu-1), [Cu(DPAA)₂(dpa)] (Cu-2), and [Cu₂(DPAA)₄(di-phen)₂] (Cu-3) were synthesized and characterized. Their antibacterial activities were evalvated. The minimum inhibitory concentrations (MIC) of these complexes against six tested microbial strains ranged from 1 to 128 μg/mL, and that of vancomycin antibiotic ranged from 0.5 to 2 μg/mL. The bactericidal effects of Cu-1, Cu-2 and Cu-3 and vancomycin against Staphylococcus aureus (S. aureus) were determined by colony count assay. Cu-1, Cu-2, and vancomycin showed relatively weaker antibiofilm formation activities; however, Cu-3 showed enhanced activity against S. aureus proliferation and biofilm formation as confirmed by microscopic analysis. In antibiofilm assays, Cu-1, Cu-2 and Cu-3 demonstrated high inhibition ability (23-75 %), of mature biofilm formation at concentrations of 5 to 15 μg/mL, and vancomycin at 15 μg/mL inhibited only 47 %. Cu-3 also effectively killed S. aureus within biofilms at doses up to 2 × MIC μg/mL. Further analysis of extracellular proteins (ECPs) expression revealed, that Cu-3 had significant potential in suppressing ECPs production. Molecular docking (MD) studies with biofilm associated protein (Bap) and SARS-CoV-2 receptors showed high interactions by several bonding types, where Cu-2 found as potent antiviral agent. Collectively, these findings highlighted the copper complexes potential in antibacterial applications, with Cu-3 emerging as a potent candidate for S. aureus biofilm inhibition.