The effect of reserpine, an inhibitor of multidrug efflux pumps, on the in-vitro activities of ciprofloxacin, sparfloxacin and moxifloxacin against clinical isolates of Staphylococcus aureus

In Staphylococcus aureus, in addition to mutations in the grl and gyr gene loci, multidrug efflux pumps like NorA contribute to decreased fluoroquinol one susceptibility. Efflux pumps can be inhibited by the plant alkaloid res erpine, which, at 20 mg/L, reduced sparfloxacin, moxifloxacin and ciproflox acin IC(50)s and MICs by up to four-fold in 11, 21 and 48 of the 102 unrela ted clinical isolates tested, respectively. The effect was less pronounced with the hydrophobic drugs sparfloxacin and moxifloxacin than with the hydr ophilic drug ciprofloxacin and was stable in all 25 clonally related isolat es tested.