P-FAH-Cu-phen's potent antimicrobial action against Escherichia coli

Escherichia coli (E. coli) infections and rising antimicrobial resistance necessitate new antibacterial strategies. Here, we characterized a copper(II)-phenanthroline complex (P-FAH-Cu-phen) and evaluated its in vitro activity and mechanism against E. coli. P-FAH-Cu-phen exhibited potent bactericidal activity, with MIC and MBC values of 1 and 2 μg/mL, respectively. Time-kill and microscopy analyses indicated rapid killing and pronounced cell-surface damage. Serial passage assays suggested a low propensity for resistance development. The complex also inhibited biofilm formation and reduced bacterial metabolic activity at MIC and sub-MIC levels. Mechanistic assays supported cell-envelope disruption, evidenced by elevated extracellular alkaline phosphatase (AKP) activity, decreased Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase activities, increased relative conductivity, and leakage of nucleic acids and proteins. Transcriptomic profiling at 30 min and 2 h revealed activation of the phenylacetate (PAA) degradation pathway and repression of purine and amino-acid biosynthesis, consistent with a multi-target stress response. Overall, P-FAH-Cu-phen exerts potent antibacterial and antibiofilm effects through combined membrane damage and metabolic perturbation, providing a mechanistic basis for further development against E. coli infections.