Accumulation of norfloxacin by Bacteroides fragilis

The accumulation of norfloxacin by Bacteroides fragilis NCTC 9343 was determined by the modified fluorescence method. The time required to achieve a steady-state concentration (SSC) after allowing B. fragilis to accumulate norfloxacin in an aerobic or an anaerobic environment was approximately 2 min; the SSC achieved in air was 90.28 +/- 9.32 ng of norfloxacin/mg (dry weight) of cells, and that achieved anaerobically was 98.45 +/- 3.7 ng of norfloxacin/mg (dry weight) of cells. Initial rates of accumulation were determined with a range of external concentrations, as up to 8 microg/ml the concentration of norfloxacin accumulated increased proportionally to the external concentration, 12.13 ng/mg (dry weight) of cells per microg of exogenous norfloxacin per ml. At concentrations above 10 microg/ml no increase in the rate of norfloxacin accumulation was observed. From the kinetic data, a Lineweaver-Burk plot calculated a K(m) of 5.03 microg/ml and a V(max) of 25.1 ng of norfloxacin/s. With an increase in temperature of between 0 and 30 degrees C, the concentration of norfloxacin accumulated also increased proportionally at 4.722 ng of norfloxacin/mg (dry weight) of cells/ degrees C. At low concentrations of glucose (