Effect of gallium nitrate on the antibacterial activity of vancomycin in methicillin-sensitive and resistant Staphylococcus aureus

The extension of multidrug-resistant strains of Staphylococcus aureus ( S.aureus ) is one of the main health challenges in the world, which requires serious solutions to deal with it. Combination therapies using conventional antibiotics and new antibacterial compounds that target different bacterial pathways are effective methods against resistant bacterial infections. Gallium is an iron-like metal that competes with iron for uptake into bacteria and has the potential to disrupt iron-dependent vital processes in bacteria. In this study, we explored the antibacterial effects of gallium nitrate (Ga(NO ₃ ) ₃ ) and vancomycin alone and in combination with each other on methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) using microdilution assay and checkerboard test, respectively. Then, their effect on the formation and destruction of biofilms was investigated. Finally, the amount of ROS production in the presence of these two compounds in bacteria was evaluated. The results indicated that the vancomycin/ Ga(NO ₃ ) ₃ combination reduced the MIC of vancomycin in the MRSA strain and had an additive effect on it. Vancomycin plus Ga(NO ₃ ) ₃ reduced the formation of biofilms and increased the destruction of biofilms formed in both strains, especially in the MRSA strain. ROS production was also higher in the combination of vancomycin with Ga(NO ₃ ) ₃ compared to vancomycin alone, especially in MRSA. Therefore, our results showed that Ga(NO ₃ ) ₃ enhances the antibacterial activity of vancomycin and this combination therapy can be considered as a new strategy for the treatment of MRSA infections.