FIGURE 4.

Transfer messenger RNA deficiency leads to higher intracellular accumulation of drugs. (A) EtBr uptake (left panel) and efflux (right panel) of R6 (wt) and R6ΔssrA (ΔssrA) strains during 20 min was measured as described in Section “Materials and Methods.” Fluorescence intensity represents levels of intracellular EtBr. The change in fluorescence is normalized to the initial levels to allow for direct comparison. Fluorescence was directly recorded during 20 min after addition of EtBr in the presence (+Res) or in the absence of reserpine. (B) Fluorometric measurement of intracellular accumulation of levofloxacin (LVX) in wt and ΔssrA at different LVX concentrations (left panel) and time points (right panel), as described in Section “Materials and Methods.” Three to five independent experiments were conducted and the mean values were statistically compared using Student’s t-test (^∗P < 0.05).