FIGURE 8.

Assay for norfloxacin accumulation in whole cells of E. coli CM2 transformants. Norfloxacin accumulation was measured in the whole cells of E. coli CM2 transformants carrying pET-mdrP (filled square) and the empty vector pET19b as a negative control (open square). Norfloxacin was used at a final concentration of 100 μM to pre-load the cells. After 25 min, CCCP was added to the cell suspensions at a final concentration of 100 μM for the disruption of transmembrane proton gradient. Each portion of cells were sampled on the indicated time points, and the intracellular accumulated norfloxacin extracted from the cells was determined by measuring the fluorescence of norfloxacin at the excitation and emission wavelengths of 277 and 448 nm, respectively. Each value point represents the average of three independent determinations.