Efflux-pump inhibitory activity of a gallotannin from Terminalia chebula fruit against multidrug-resistant uropathogenic Escherichia coli

This study was carried out to evaluate the possible efflux-pump inhibitory activity of a gallotannin 1,2,6-tri-O-galloyl-β-d-glucopyranose isolated from Terminalia chebula fruit against multidrug-resistant (MDR) uropathogenic Escherichia coli. Susceptibility tests of antibiotics and ethidium bromide in the presence and absence of isolated gallotannin and phenylalanine-arginine β-naphthylamide (PAβN) were conducted by using the microbroth dilution assay. Ethidium bromide accumulation and efflux assays were performed spectrofluorometrically to elucidate the possible resistance-modifying activity of isolated gallotanin, if any. Minimum inhibitory concentrations of test antibiotics and ethidium bromide were reduced in the presence of isolated gallotannin and PAβN. The isolated gallotannin also demonstrated efflux-pump inhibitory activity against the studied bacteria as evidenced from ethidium bromide accumulation and efflux assays. The isolated gallotannin, 1,2,6-tri-O-galloyl-β-d-glucopyranose exhibited efflux-pump inhibitory activity which may be one of the possible mechanisms of its antibacterial action against MDR uropathogenic E. coli.