FIG. 2.

Functional analyses of MdfA mutants. E. coli cells transformed with empty vector (vec) or plasmids encoding wild-type MdfA (WT) or the indicated MdfA mutants were diluted as marked [Dilution (-log)] and spotted onto LB agar plates with or without the test drug, and plates were visualized after ∼20 h at 37°C. LD₅₀ measurements with chloramphenicol (CAM) and EtBr (4) are indicated (in micrograms/milliliter) on the right. (B) Cells expressing the indicated mutants were loaded with EtBr and energized with glucose (left arrow), and the EtBr efflux was monitored continuously in the fluorimeter. As expected, the addition of carbonyl cyanide m-chlorophenylhydrazone (CCCP) (right arrow) abolished efflux. The experiments were repeated at least three times, and the results shown are representative. a.u., arbitrary units.