Toward a Molecular Understanding of the Antibacterial Mechanism of Copper-Bearing Titanium Alloys against Staphylococcus aureus

The antibacterial mechanism of the Cu-containing materials has not been fully understood although such understanding is crucial for the sustained clinical use of Cu-containing antibacterial materials such as bone implants. The aim of this study is to investigate the molecular mechanisms by which the Gram-positive Staphylococcus aureus is inactivated through Cu-bearing titanium alloys (Ti6Al4V5Cu). Cu ions released from the alloys are found to contribute to lethal damage of bacteria. They destroy the permeability of the bacterial membranes, resulting in the leakage of reducing sugars and proteins from the cells. They also promote the generation of bacteria-killing reactive oxygen species (ROS). The ROS production is confirmed by several assays including fluorescent staining of intracellular oxidative stress, detection of respiratory chain activity, and measurement of the levels of lipid peroxidation, catalase, and glutathione. Furthermore, the released Cu ions show obvious genetic toxicity by interfering the replication of nuc (species-specific) and 16SrRNA genes, but with no effect on the genome integrity. All of these effects lead to the antibacterial effect of Ti6Al4V5Cu. Collectively, our work reconciles the conflicting antibacterial mechanisms of Cu-bearing metallic materials or nanoparticles reported in the literature and highlights the potential use of Ti6Al4V5Cu alloys in inhibiting bacterial infections.