New rapid bioassay of gentamicin based on luciferase assay of extracellular ATP in bacterial cultures.

Bacterial ATP levels in Escherichia coli cultures were determined by luciferin/luciferase assay. Rapid effects of gentamicin on ATP levels in the cultures were studied, and a dose-dependent accumulation of extracellular ATP was demonstrated. This phenomenon was used to develop a rapid bioassay of gentamicin in clinical serum specimens. The accuracy of the assay, expressed as coefficient of variation over the range 16 to 1 mug/ml, varied between 1.8 and 6.5%, compared to 2.3 to 4.7% for an agar disk diffusion assay. Serum gentamicin concentrations were determined by both methods in 122 serum specimens from 43 patients receiving gentamicin alone or in combination with other antibiotics, and the results were compared (r = 0.942). Determination of gentamicin based on luciferase assay of extracellular ATP in bacterial cultures requires only 10 mul of serum, allowing for capillary sampling, and results are available within 2 h.