Combined systems of different antibiotics with nano-CuO against Escherichia coli and the mechanisms involved

Aim: The combined efficacy of CuO nanoparticles (NPs) with 22 kinds of antibiotics against Escherichia coli was systematic studied, and CuO with cephalexin synergistic system was screened out. Methods: Antimicrobial susceptibility test included disk diffusion test, checkerboard method and time-kill assay. The interactions of CuO NPs and antibiotics were analyzed by x-ray photoelectron spectroscopy, Fourier transform infrared spectra and Zeta. The interactions between bacteria and antibacterial agents were studied by surface plasmon resonance sensor for the first time. Results & Conclusion: Synergistic effect (1+1>2) was observed when CuO NPs combined with cephalexin against E. coli. The concentrated cephalexin molecules interacted more strongly with the E. coli cells to make cell wall become loose. Then, CuO NPs were more easily to damage and penetrate cells. Besides, the presence of antibiotics did not enhance Cu2+ release, Cu2+ uptake and reactive oxygen species generation. But the presence of cephalexin greatly enhanced cell permeability in comparison to others.