MepA-mediated efflux of EtBr. Bars: 1, SA-K1758-P; 2, SA-K1758-P with reserpine (20 μg/ml); 3, SA-K1758-A; 4, SA-K1758-A with reserpine. Results are expressed as percent reduction in fluorescence (means ± standard deviations), which correlates with EtBr efflux, over 5 min.