Copper(II) enhances the antibacterial activity of nitroxoline against MRSA by promoting aerobic glycolysis

Nitroxoline (NIT) is an FDA-approved antibiotic with numerous pharmacological properties. However, the intricate connections between its metal-chelating ability and antimicrobial efficacy remain incompletely understood. The specific interactions of NIT with different metal ions were measured via UV–vis absorption spectroscopy. Here, we found that NIT can bind to various metal ions, including Cu²⁺, Fe²⁺, Zn²⁺ and Mn²⁺. However, the antimicrobial activity of NIT against methicillin-resistant Staphylococcus aureus (MRSA) was significantly enhanced by the inclusion of Cu²⁺ as determined by a minimal inhibitory concentration (MIC) assay in Mueller-Hinton broth. The enhanced antibacterial effect was not influenced by the availability of oxygen. Mechanistically, Cu²⁺ promoted bacterial proliferation, increased the bacterial transmembrane electrical potential, and increased intracellular acidification. In addition, Cu²⁺ rewired bacterial metabolism, promoting the uptake of glucose with a lower level of ATP production. Pharmacological upregulation of glycolysis by VLX600 could potentiate the susceptibility of MRSA to NIT. Moreover, Cu²⁺ also significantly increased the survival rate of acutely infected larvae. These collective results underscore that the enhanced antibacterial efficacy of NIT by Cu²⁺ intricately involves aerobic glycolysis in MRSA.