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 fluoroquinolone susceptibility. Efflux pumps can be inhibited by the plant alkaloid reserpine, which, at 20 mg/L, reduced sparfloxacin, moxifloxacin and ciprofloxacin IC50s and MICs by up to four-fold in 11, 21 and 48 of the 102 unrelated clinical isolates tested, respectively. The effect was less pronounced with the hydrophobic drugs sparfloxacin and moxifloxacin than with the hydrophilic drug ciprofloxacin and was stable in all 25 clonally related isolates tested.