Erythromycin and Azithromycin Transport into Haemophilus influenzae ATCC 19418 under Conditions of Depressed Proton Motive Force (A'H)

The effect of collapsing the electrochemical proton gradient (AjiH) on [3H]erythromycin and ['4C]azithromycin transport in Haemophilus influenzae ATCC 19418 was studied. The proton gradient and membrane potential were determined from the distribution of [2-14C]dimethadione and rubidium-86, respectively. A.LH was reduced from 124 to 3 mV in EDTA-valinomycin-treated cells at 22°C with 150 mM KCI and 0.1 mM carbonyl cyanide m-chlorophenylhydrazone. During the collapse of A(LH, macrolide uptake increased. Erythromycin efflux studies strongly suggested that this increase was not due to an energy-dependent efflux pump but was likely due to increased outer membrane permeability. These data indicated that macrolide entry was not a AiiH-driven active transport process but rather a passive diffusion process.