Fluorometric assay for fleroxacin uptake by bacterial cells

A sensitive and convenient method for quinolone determination has been developed, based on the natural fluorescence of the quinolone nucleus. Fleroxacin (Ro 23-6240; AM 833), used as a prototype quinolone in these studies, had an excitation maximum at 282 nm and an admission maximum at 442 nm (pH 3.0). Fluorescence intensity was pH dependent, being maximal at pH 3.0 and linear at quinolone concentrations between 1 and 200 ng/ml. A protocol for the fluorometric monitoring of fleroxacin uptake in Escherichia coli was developed. Intracellular quinolone concentrations measured by the fluorometric assay correlated well with values obtained by the bioassay. The results indicate that the fluorometric assay is an attractive alternative to the more laborious bioassay.