Green, novel, and one-step synthesis of silver oxide nanoparticles: antimicrobial activity, synergism with antibiotics, and cytotoxic studies

Abstract

Silver oxide nanoparticles (Ag₂ONPs) were synthesized by a one-step, green, and novel method. Ag₂ONPs were characterized independently as well as in mixtures with common antibiotics. The antibacterial activity of Ag₂ONPs and antibiotics was evaluated by the minimum inhibitory concentration method and the effect of the combination by the checkerboard assay against representative reference strains and five multidrug-resistant (MDR) bacteria, which were isolated from patients with skin wound infections. The viability and cytotoxic effects were evaluated on human dermal fibroblasts (HDF) by the calcein/EthD-1 method and the MTT assay. TEM analysis showed that the Ag₂ONPs are spherical with an average size of 8.72 nm and zeta potential of −63.68 mV. The XRD diffractogram revealed that Ag₂ONPs have a cubic crystal structure, and the Raman spectrum confirmed the characteristic vibrational modes of the structure. FT-IR spectra suggest that Ag₂ONPs interact with amino and carboxyl groups present in antibiotics. It was found that Ag₂ONPs have a broad-spectrum antibacterial effect, and a concentration of less than 8 μg mL⁻¹ was required to inhibit the development of MDR bacteria. Both basic antibiotics were able to enhance the antimicrobial effect of Ag₂ONPs; however, combination with ciprofloxacin showed that concentrations <1 μg Ag₂ONPs per mL inhibit the growth of all the tested bacteria. The calcein/EthD-1 method revealed that concentrations ≤1 μg Ag₂ONPs per mL are tolerated by HDF, showing their characteristic phenotype, while the MTT assay showed that concentrations ≤0.5 μg Ag₂ONPs per mL do not affect cell proliferation during four days in culture. Ag₂ONPs used in this study were biocompatible with HDF and inhibit the growth of MDR bacteria, properties that were improved in combination with commercial antibiotics, suggesting that these combinations could be used to prevent infections of skin wounds by MDR bacteria and their dissemination.