Atividade antimicrobiana e efeito sinérgico de complexos de rutênio fotoirradiados contra células planctônicas e biofilmes de Staphylococcus spp

Abstract

Antimicrobial resistance is a critical global public health problem. Many bacterial infections are associated with the ability of microorganisms to form biofilms, which is essential for colonization of the most diverse environments, in addition to conferring high levels of resistance. Faced with this problem, the discovery of new classes of molecules that have an antimicrobial effect constitutes a target to be achieved. The aim of this study was to evaluate

the antibacterial, antibiofilm and synergistic effect of ruthenium complexes [Ru(phen)2(bpy- ant)]2 + and [Ru(bpy)2(bpy-ant)]2+, called Ru-P and Ru-B, and their combined effects with

antibiotics against Staphylococcus aureus ATCC 25923, Staphylococcus aureus ATCC 700698, Staphylococcus epidermidis ATCC 12228 and Staphylococcus epidermidis ATCC 35984 strains. To determine antibacterial activity, 100 μL of ruthenium complex in different concentrations (250-1.9μg/mL) for Minimum Inhibitory Concentration and Minimum Bactericidal Concentration, and (125-1.9 μg/mL), for the other biomass quantification (CV) and Colony Forming Units counts (UFC), were distributed in non-irradiated flat-bottomed 96- well plates for MIC assays, and irradiated with blue LED for 60 minutes. To test the cytotoxicity of the complexes, strains of murine fibroblasts, L929, were used together with different concentrations of the complexes (125-1.9 μg/mL) and evaluated for 24, 48 and 72 hours. The antimicrobial effect of ruthenium complexes was evaluated by CIM and CBM. To realize the effect of the combination between complexes and antibiotics, the MIC values were combined with the antibiotics ampicillin and tetracycline and their effects were evaluated using the checkboard technique. The antibiofilm activity of the Ru-P and Ru-B complexes was verified on the formation of biofilms and preformed biofilms by quantifying the biomass by the crystal violet (CV) staining method and by the number of viable cells of the biofilms by means of of colony forming units (CFU) counts. The Ru-P and Ru-B complexes exhibited differences in antimicrobial activity between irradiated with blue LED, with MIC and CBM values ranging between 1.9 and 3.9 μg/mL, and non-irradiated with MIC values ranging between 15, 6 and 250 μg/ml. The synergistic effect against Staphylococcus spp. was observed when these complexes were combined with ampicillin and tetracycline, exhibiting Fractional Inhibitory Concentration Index (FICI) values ranging from 0.125 to 1.0. Regarding the activity on biofilm formation, the complexes were able to reduce biomass by more than 30% at a concentration of 1.9 μg/mL and 100% at a concentration of 125 μg/mL. The number of viable cells of biofilms was reduced between 1.5 and 8 logs. Regarding the activity on pre-formed biofilms, the complexes were able to reduce the biomass from 12 to 41% at the highest concentration tested. The number of viable cells in the biofilms was reduced by less than 1 log. The Ru-P complex presented cytotoxicity greater than 50%, at concentrations above 31.2 μg/mL, and above 30%, at concentrations from 125 to 62.6 μg/mL, at the tested exposure times, 24, 48 and 72 hours. The Ru-B complex showed cytotoxicity below 50% at all tested concentrations and at all tested exposure times. The ruthenium complexes showed antimicrobial and antibiofilm activity against Staphylococcus aureus and Staphylococcus epidermidis, and showed a synergistic effect when combined with ampicillin and tetracycline antibiotics. These results demonstrate that the ruthenium complexes tested in this study have the potential to help therapies for the treatment of bacterial infections caused by Staphylococcus spp.