Objective: A reversed-phase high performance liquid chromatographic method was described for the determination of ciprofloxacin (CPLX) in 4 strains of enteric bacilli. Methods: Ciprofloxacin was added to the bacterial suspension

and the culture was incubated at 37℃ with shaking. At appropriate time intervals 1ml samples were removed and treated by ultrasonic wave. The concentration of CPLX in the supernatants was measured by HPLC assay. Samples were analysed on an ODS-C18 column with a mobile phase of methand-0.008M phosphate buffer -0.5M tetrabulylammonium bromide (25:75:4

v/v/v). A fluorescence detecter was used. Excitation and emission wavelenth were 278nm

445nm

respectively. Results: The detection limit was 0.06mg/L. Good linearity was obtained in the concentration range from 0.154 to 12.5mg/L with the correlation coefficient (r=0.9997). The variant rates of within-day and day- to- day were 2.66% and 4.15% respectively. The uptake curve showed that all strains attained peak concentration at 10 minutes. Conclusion: HPLC assay for CPLX uptake by enteric bacilli is better for measuring drug concentrations because of lesser interference from other bioactive substances in cell extracts. So it may be a good way to study of fluoroquinolone resistant mechanisms.