FIG. 3.

Accumulation of [³H]tetracycline by intact cells of P. aeruginosa PAM1275 (●, ○) and PAM1275(pAGH97) (⧫, ◊). The MICs of tetracycline for PAM1275 and PAM1275(pAGH97) were 2 and 16 μg ml⁻¹, respectively. The cells were prepared as described in the legend to Fig. 2. After 5 min at 37°C, a mixture of tetracycline and [³H]tetracycline (0.55 Ci mmol⁻¹) was added to a final concentration of 2 μg ml⁻¹; and the samples were taken and filtered, and the radioactivity was counted. After 7.5 min of incubation, a 500 μM final concentration of CCCP was added to one-half of the reaction mixture. Accumulation in CCCP-treated samples is represented by open symbols, and that in samples that did not receive CCCP is indicated by closed symbols. The data are means for three independent experiments. No modification of intracellular accumulation of antibiotic was observed when strains were transformed with pAK1900.