Antimicrobial Activity of Microgels with an Immobilized Copper(II) Complex Linked to Cross-Linking and Composition

The resistance of many bacteria against currently available antimicrobial agents is increasing worldwide at an alarming pace. The described structure-activity relationship study was prompted by the extraordinary ability of water-dispersed microgels to hydrolyze glycosidic bonds similar to building blocks of the peptidoglycan layer of Gram-positive bacteria. The results establish polyacrylate microgels with embedded copper(II) complex as antimicrobial agents. The systematic study reveals that Staphylococcus aureus is susceptible to the microgels, while common commercial agents are found intermediate or resistant. In particular, a microgel with 60 mol % of cross-linking, ^Cu₂^LP_60%, shows intriguing bactericidal activity at 1 μg/mL, while vancomycin requires a 4-fold higher dose, i.e., 4 μg/mL, for the same effect. The minimum inhibitory concentration of ^Cu₂^LP_60% was determined as low as 0.64 μg/mL. Excellent stability of the poly(acrylate) microgels was observed by negative zeta potentials in nanopure water and aqueous sodium dodecyl sulfate solution. The composition of the microgel matrix with embedded binuclear metal complex was shown to be responsible for the antimicrobial activity, while the aqueous buffer-surfactant solution is not.