Effect of sodium chloride on gentamicin accumulation by Escherichia coli: Correlation with bacterial growth and viability

The kinetics of gentamicin accumulation by a sensitive strain of Escherichia coli were investigated at gentamicin concentrations from 0.02 to 200 microgram/ml. Accumulation with time shows two energy-dependent phases and is saturable. Sodium chloride delays the onset of the second more rapid energy-dependent phase and decreases the magnitude of gentamicin accumulation for incubations up to 60 minutes at all gentamicin concentrations tested. Simultaneous determinations of accumulation, cell viability, and growth inhibition indicate that antimicrobial activity is correlated with the magnitude of gentamicin accumulation. These observations suggest that altered bacterial accumulation of gentamicin explains the effect of sodium chloride on the antimicrobial activity of gentamicin.