Oxidative Stress and Antimicrobial Activity of Chromium(III) and Ruthenium(II) Complexes on Staphylococcus aureus and Escherichia coli

Abstract

The prevalence of antibiotic resistance has resulted in the need for new approaches to be developed to combat previously easily treatable infections. The main aim of this work was to establish the potential of the synthetic alfa-diimine chromium(III) and Ruthenium(II) complexes (where the alfa-diimine ligands are bpy = 2,2-bipyridine; phen = 1,10-phenanthroline and dppz = dipyrido[3,2-a:2´,3´-c]-phenazine) like [Cr(phen)3]3+, [Cr(phen)2(dppz)]3+, [Ru(phen)3]2+ and [Ru(bpy)3]2+ as antibacterial agents by generating oxidative stress. The [Cr(phen)3]3+ and [Cr(phen)2(dppz)]3+ complexes showed activity against Gram positive and Gram negative bacteria with minimum inhibitory concentrations (MICs) ranging from 0.125 µg/mL to 1 µg/mL, while [Ru(phen)3]2+ and [Ru(bpy)3]2+ does not exhibit antimicrobial activity against the two bacterial genera studied at the concentration range used. When ciprofloxacin was combined with [Cr(phen)3]3+ for the inhibition of Staphylococcus aureus and Escherichia coli, an important synergistic effect was observed, FIC 0.066 for S. aureus and FIC 0.064 for E. coli. The work described here shows that chromium(III) complexes are bactericidal for S. aureus and E. coli. Our results indicate that alfa-diimine chromium(III) complexes may be interesting to open new paths for metallodrug chemotherapy against different bacterial genera since some of these complexes have been found to exhibit remarkable antibacterial activities.