Synergistic antibacterial study of nano-Cu2O/CuO@Ag-tetracycline composites

The rapid increase in drug resistance has not reduced the antibacterial activity of most antibacterial drugs but also brought great challenges to society. Therefore, there is an urgent need to develop new antibacterial agents. In this study, copper nitrate trihydrate [Cu(NO3)2·3H2O] was used as a raw material and hydrazine hydrate as a reducing agent to prepare cuprous oxide (Cu2O/CuO). Next, silver nitrate (AgNO3) was added and monomeric silver was loaded on the surface of Cu2O by in situ reduction to obtain Cu2O/CuO@Ag composites. Lastly, nano-Cu2O/CuO@Ag-tetracycline composites were obtained by combining them with tetracycline. Systematic characterization of inhibitors was conducted using transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), and ultraviolet–visible spectroscopy (UV–vis). The inhibitory properties and mechanism of Cu2O/CuO@Ag-tetracycline on the Gram-positive bacterium Staphylococcus aureus (S. aureus), Gram-negative bacterium Escherichia coli (E. coli), and drug-resistant bacterium Salmonella (T-Salmonella) were studied. The inhibition performance study showed that the inhibition rate of Cu2O@CuO@Ag-tetracycline was almost 99.99% against the three tested bacteria at 40 min when used at a concentration of 150 μg/mL. Compared with tetracycline and Cu2O/CuO alone, Cu2O/CuO-tetracycline composites have several times higher antibacterial efficiency against E. coli, S. aureus and T-Salmonella. Moreover, the nano-Cu2O/CuO@Ag-tetracycline composites were most sensitive to E. coli. The inhibition mechanism revealed that the nanocomposites could effectively destroy the cell wall of Gram-negative bacteria, enter the cell interior, inhibit cell respiration, and eventually lead to bacterial rupture and death. The nano-Cu2O/CuO@Ag-tetracycline composites exhibited excellent antibacterial properties, indicating their wide application prospects in the fields of medical devices and medical materials.