Discovery of quaternized pyridine-thiazole-ruthenium complexes as potent anti-Staphylococcus aureus agents

Quaternization of ruthenium complexes may be a promising strategy for the development of new antibiotics. In response to the increasing bacterial resistance, we integrated the quaternary amine structure into the design of ruthenium complexes and evaluated their antibacterial activity. All the ruthenium complexes showed good antibacterial activity against the tested Staphylococcus aureus (S. aureus). Ru-8 was the most effective antibacterial agent that displayed excellent antibacterial activity against S. aureus (MIC = 0.78-1.56 μg/mL). In vitro experiments showed that all nine ruthenium complexes had low hemolytic toxicity to rabbit erythrocytes. Notably, Ru-8 was found to disrupt bacterial cell membranes, alter their permeability, and induce ROS production in bacteria, all the above leading to the death of bacteria without inducing drug resistance. To further explore the antibacterial activity of Ru-8in vivo, we established a mouse skin wound infection model and a G. mellonella larvae infection model. Ru-8 exhibited significant antibacterial efficacy against S. aureus in vivo and low toxicity to mouse tissues. The Ru-8 showed low toxicity to Raw264.7 cells (mouse monocyte macrophage leukemia cells). This study indicates that the ruthenium complex ruthenium quaternary was a promising strategy for the development of new antibacterial agents.