E. coli aminoglycoside treatment

Aminoglycosides are broad-spectrum antibiotics whose mechanism of action is under debate. It is widely accepted that membrane voltage potentiates aminoglycoside activity, which is ascribed to voltage-dependent drug uptake. In this paper, we measured the response of Escherichia coli treated with aminoglycosides and discovered that the bactericidal action arises not from the downstream effects of voltage dependent drug uptake, but rather directly from dysregulated membrane potential. In the absence of voltage, aminoglycosides are taken into cells and exert bacteriostatic effects by inhibiting translation. However, cell killing was immediate upon re-polarization. The hyperpolarization arose from altered ATP flux, which induced a reversal of the F1Fo-ATPase to hydrolyze ATP and generated the deleterious voltage. Heterologous expression of an ATPase inhibitor completely eliminated bactericidal activity, while loss of the F-ATPase reduced the electrophysiological response to aminoglycosides. Our data support a model of voltage induced death, and separates aminoglycoside bacteriostasis and bactericide in E. coli.

Methods
Data was collected on an inverted fluorescence microscope using a 488 nm and 561 nm excitation.  Raw data was pre-processed by correcting uneven illumination, registering frames in time, and subtracting an estimated background.  Each cell has a time trace that is provided here, and each cell is part of a population that represents 1 biological replicate.  Each biological replicate comes from an indepenently grown and imaged population of bacteria.