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.