Modulação da resistência a drogas por Furocumarinas e Furocromonas em Staphylococcus aureus

Abstract

Microbial resistance to antibiotics has become a worldwide crisis problem, requiring the search for inhibitors of resistance mechanisms that can re-establish the usefulness of these compounds. Furocoumarins and furochromones are natural substances with several important biological properties, such as antibacterial, anti-inflammatory, antitumor, and others. In the present work, substances from the class of furocoumarins and furochromones were evaluated as modulators of drug resistance by inhibition of bacterial efflux systems. The BHI broth microdilution technique was used to determine the minimum inhibitory concentration (MIC) of the compounds against Staphylococcus aureus strain SA-1199B overexpressing the NorA efflux protein. The compounds Ciprofloxacin, Norfloxacin, Ethidium bromide (EtBr), and Berberine were used as NorA substrates to evaluate the modulating action of the substances. No furocoumarin and furochromone tested showed relevant antibacterial activity (MIC ≥512 μg/mL) against S. aureus SA-1199B. However, all showed drug resistance modulating activity. In the modulation assay, the furocoumarins and furochromones were incorporated into the culture medium at subinhibitory concentration (¼ of the MIC). The furocoumarin Isosaxalin showed the best result, modulating 8-fold the minimum inhibitory concentration (MIC) of Norfloxacin, Heraclenol modulated 4-fold and the other furocoumarins (Psoralen, Angelicin, and 3-Carbethoxypsoralen) modulated 2-fold, both, for Norfloxacin and Ciprofloxacin. The furochromones Khellin and Visnagin modulated 2-fold the MIC of Norfloxacin and Ciprofloxacin. The modulation result was similar to EtBr and Berberine indicating that these substances are possible efflux pump inhibitors (EPIs). To understand the differences in their abilities to act as EPIs, a molecular docking study of the furocoumarins and furochromones against the NorA pump model was conducted. Through molecular docking it was possible to theoretically verify the interaction of these substances with the NorA pump, corroborating the microbiological study.