Synthesis of CuO and ZnO nanoparticles by a novel green route: Antimicrobial activity, cytotoxic effects and their synergism with ampicillin

CuO and ZnO nanoparticles (NPs) were synthesized at room-temperature following a novel, direct, high-yield (>91%) and green method based on a mechanically activated metathesis reaction. The CuO-NPs exhibited a rod-like shape with average length and diameter of 22 and 6 nm, respectively, while the ZnO-NPs showed spherical-like morphology and mean diameter of 15 nm, as determined by TEM. The antimicrobial properties of the NPs and commercially available micrometric counterparts were evaluated by the micro dilutions method to determine the minimum inhibitory concentrations against reference strains from ATCC microorganisms, which were representative of the main groups of bacteria related to human infections, such as E. coli, S. aureus, E. faecalis and P. aeruginosa. The CuO and ZnO-NPs showed better antibacterial properties (500 μg/mL) in comparison with the commercial micrometric particles (1000 μg/mL). The analysis of the synergism between both NPs and ampicillin showed a decrease of their concentrations against all the microorganisms studied, with the ZnO-NPs showing better synergism activity than CuO-NPs, whereas the combination of the antibiotic with ZnO-NPs showed a six-fold decrease against all the microorganisms studied except to P. aeruginosa. The FIC index was calculated with both NPs and ampicillin to each bacterium. In most cases, the effect was partial synergism, and an additive effect was achieved when those combinations were evaluated against P. aeruginosa. The cell viability tests showed that the CuO and ZnO-NPs synthesized and mixed with the antibiotic are biocompatible in effective doses (<25 μg/mL). The NPs used in this study, prepared by a green innovative synthesis, and their combination with a basic antibiotic showed interesting results, suggesting the possibility of one alternative to biological applications.