Antibacterial activity and effect on the outer membrane permeability of Apis mellifera honey from Brazil

This study evaluates the antibacterial activity of Apis mellifera honey (in fresh form and in extracted fractions) and its effects on the outer membrane permeability of Enterococcus faecalis and Staphylococcus epidermidis. Five honey samples from four municipalities in the Midwest of Brazil (Mato Grosso state) were evaluated in this study. Samples of fresh honey and its hexane, ethyl acetate, and n-butanol fractions were prepared by the fractional extraction method in a separating funnel using each fraction's solvent. Antibacterial activities were assessed using the broth microdilution method with serial dilution of the samples ranging from 1000 to 1.95μg/ml. Outer membrane permeability was determined by the broth microdilution method with a combination of honey or solvent extract fraction (80-0.15mg/ml) and clarithromycin and erythromycin (20-0.04μg/ml) prepared in a checkerboard. Time-kill assays were performed at 2, 4, 8 and 24h. At a concentration of 1000μg/ml, no antibacterial activity was observed, with inhibition below 24% for two bacteria. Honey 1 (80mg/ml) and its n-butanol fraction increased the outer membrane permeability of E. faecalis when combined with clarithromycin (20μg/ml), but no effect on membrane permeability of E. faecalis was observed for the remaining r four honey samples and their fractions. None of the samples affected the membrane permeability of S. epidermidis. We concluded that honey 1 increase the antibacterial activity of clarithromycin and erythromycin against E. faecalis, possibly due to the action of flavonoids.