The accumulation of fluoroquinolones in Staphylococcus aureus during the postantibiotic effect.

The accumulation of radiolabelled pefloxacin, norfloxacin, and lomefloxacin was determined in Staphylococcus aureus during log phase growth, the postantibiotic effect (PAE), and at 1, 4 and 6 h post PAE. Uptake in actively growing cells was consistent with a non-saturable passive diffusion process. The addition of metabolic inhibitors significantly increased accumulation consistent with the presence of an energy dependent efflux system. Accumulation of all three fluoroquinolones in PAE phase cells was significantly increased compared to that which occurred in actively growing cells. In contrast to cells in the log phase, addition of metabolic inhibitors to PAE phase cells did not result in a significant increase in drug accumulation. Uptake kinetics 1 h and 4 h post PAE were similar to those found during the PAE phase. Organisms required 6 h after the end of the PAE phase before normal uptake kinetics of fluoroquinolones resumed.