Structural and Microbiological Characterization of 5-Hydroxy-3,7,4′-Trimethoxyflavone: A Flavonoid Isolated from Vitex gardneriana Schauer Leaves

Introduction: Staphylococcus aureus represents the most common etiologic agent of purulent infections, affecting humans and animals. Escherichia coli is one of the principal causes of infectious diseases, mainly diarrheal diseases due to enterotoxin action. There are many reports indicating that these bacteria are multidrug-resistant (MDR) pathogens. Objective: In this study, we investigated the antimicrobial and modulatory activities of 5-hydroxy-3,7,4 '-trimethoxyflavone (VG.EF.CLII) against E. coli and S. aureus strains. Methods: 5-Hydroxy-3,7,4 '-trimethoxyflavone was isolated from Vitex gardneriana Schauer leaves and structurally characterized using nuclear magnetic resonance. The antibacterial effect of VG.EF.CLII and modulation of antibiotic activity, both determined by minimum inhibitory concentration, were assessed using microtiter plates. Results: VG.EF.CLII showed bacterial growth inhibition at concentrations <= 512 mu g/mL, and synergistic effects were observed for the modulation of two distinct antibiotic classes (the fluoroquinolone norfloxacin and the aminoglycoside gentamicin). Conclusion: 5-Hydroxy-3,7,4 '-trimethoxyflavone isolated from V. gardneriana showed promising antimicrobial activity against MDR bacterial strains S. aureus 358 and E. coli 27 when associated with the antibiotics norfloxacin and gentamicin. Therefore, this natural product can contribute to the control of bacterial resistance.