FIG. 4.

Efflux from NorA-overexpressing (K2378 NorA++) S. aureus cells of ethidium bromide (⧫); ethidium bromide in the presence of INF55 (⋄); and ethidium bromide in the presence of hybrids SS14 (▴) (31), SS14-M (▪), and SS14-P (•). Cells were initially preloaded with ethidium bromide in the presence of the MDR inhibitor reserpine (26) to prevent the loss of ethidium bromide. Hybrids or INF55 in dextrose buffer was added to the cells after they had been washed to remove the reserpine. Efflux was measured by monitoring the decreases in fluorescence at 600 nm (excitation at 530 nm) and is expressed as arbitrary units (A.U.). All compounds were present at a final concentration of 3 μM. The graph is representative of at least three independent experiments. Berberine alone had no effect on ethidium bromide efflux (data not shown).