Role of the membrane potential in bacterial resistance to aminoglycoside antibiotics.

The electrical potential difference (delta psi) across the membrane of Escherichia coli was measured by the distribution of lipid-soluble cations and correlated with resistance to dihydrostreptomycin, where resistance is presumed due to reduced uptake of the drug. A good correlation between the two measured parameters was found under all conditions tested, which included effects of several mutations, inhibitors, changes in pH, and osmolarity. The most dramatic changes were seen when pH was varied; in wild-type strains resistance increased more than 100-fold, and delta psi fell by 70 mV when pH was reduced from 8.

Thallous ion is accumulated by potassium transport systems in Escherichia coli.

The accumulation of 204T1+ by Escherichia coli occurs primarily via either of two K+ transport systems called Kdp and TrkA. T1+ influx is inhibited and T1+ efflux is stimulated by the addition of K+ to the assay medium. Mutants defective in both the Kdp and TrkA systems accumulate little T1+.