Atividade antimicrobiana e efeito combinado com antibióticos do nitro complexo de rutênio [RuCl(NO2)(dppb)(4,4’-Mebipy)] na presença e na ausência de luz azul

Abstract

Antimicrobial resistance (AMR) is a critical global public health problem. The biofilm formation is one of the main virulence factors of AMR and plays an important role in more than 80% of bacterial infections and 65% of hospital infections. In this study, we investigated the antimicrobial activity, the combined effect with antibiotics, the interaction with DNA and the cytotoxic activity of the ruthenium nitro complex [RuCl(NO2)(dppb)(4,4-Mebipy)] (designated RuNO2) irradiated with blue light and in the absence of irradiation.. The effect of the complex against planktonic cells was evaluated by determining the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The combined effect with antibiotics was verified by the checkerboard technique. Antibiofilm activity was evaluated by total biomass quantification, viable cell counting, confocal microscopy and scanning electron microscopy (SEM). Finally, the interaction with DNA and cytotoxicity against human erythrocytes and murine fibroblasts (L929) were verified by electrophoresis, hemolytic activity and cell viability assay (MTT), respectively. In general, the compound showed antimicrobial activity against Gram-positive and Gram-negative bacteria, with MIC and MBC values ranging from 4 to 256 μg/ml, both photoirradiated and without irradiation. The synergistic effect against Staphylococcus aureus and Staphylococcus epidermidis was observed when the complex was combined with ampicillin, presenting FICI values between 0.186 and 0.311, however, when associated with tetracycline, RuNO2 showed a synergistic effect only against Pseudomonas aeruginosa and Escherichia coli. In the biofilm assay, a reduction of between 65% and 99.8% in total biomass and a decrease of between 1 and 4 orders on the logarithmic scale in the number of viable cells were observed. SEM and Confocal analyzes revealed changes in cell morphology, damage to the wall and plasma membrane of S. aureus and E. coli. In DNA cleavage assays, the compound showed no evidence of effect in the absence of photoirradiation but promoted efficient DNA cleavage when irradiated by blue light. On human erythrocytes RuNO2, it presented a percentage of hemolysis between 2 and 4% only at the highest concentrations tested and, on murine L929 cells, there was no toxicity since at both times evaluated, the treated cells did not show viability less than 50%. Taken together, these results summarize the potential of this complex, which deserves further investigation.