COMPARATIVE EVALUATION OF ANTIBIOTIC AND ANTIBIOTIC MODIFYING ACTIVITY OF QUERCETIN AND ISOQUERCETIN IN VITRO

The use of secondary metabolites with biological properties, such as flavonoids, has been increasingly documented. This work evaluates the in vitro antibiotic activity of two flavonoids: quercetin and isoquercetin. The microdilution broth test was used to measure antimicrobial activity against standard and multiresistant strains of E. coli and S. aureus and strains of Candida. These flavonoids were also tested for a modulatory effect on aminoglycoside antibiotics. The flavonoids studied did not show significant antibacterial activity, while only isoquercetin demonstrated notable antifungal activity, inhibiting the growth of Candida krusei at a concentration of 32 mu g/mL. In relation to modifying activity, there was no potentiation of the antibiotics tested. Isoquercetin showed antagonism with all the aminoglycosides examined, considerably increasing their minimal inhibitory concentrations (MICs). In light of these results, more in-depth studies are necessary, aimed at standardizing the protocols of antibiotic assays, as well as evaluating the effect of test substances against other classes of antimicrobials.