Rapid bioluminescent assay for determining netilmicin and tobramycin concentrations in serum

A rapid bioluminescent assay for determining netilmicin and tobramycin concentrations in serum based on the dose-dependent effect of these agents on the accumulation of extracellular ATP in Escherichia coli LU 14 cultures is presented. This strain of Escherichia coli is unaffected by antibiotics used in combination with aminoglycosides and it lacks significant ATP-ase activity, which is a prerequisite for extracellular ATP accumulation. ATP was quantified by the firefly bioluminescence system. The accuracy of the bioluminescent assay expressed as mean coefficient of variation over the therapeutic range was 3.2%; corresponding figures for EMIT and an agar disk diffusion assay were 4.2% and 4.8% respectively. All methods used correlated well (r = 0.935-0.986) when they were evaluated on clinical serum specimens. The bioluminescent assay requires 25 microliters serum and results are available within 75 min.