The AcrAB-TolC pump is involved in macrolide resistance but not in telithromycin efflux in Enterobacter aerogenes and Escherichia coli

Abstract

The role of the AcrAB-TolC pump in macrolide and ketolide susceptibility in Escherichia coli and Enterobacter aerogenes was studied. Efflux pump inhibitor restored erythromycin, clarithromycin, and telithromycin susceptibilities to multidrug-resistant isolates. No modification of telithromycin accumulation was detected in E. aerogenes acrAB or tolC derivatives compared to that in the parental strain. Two independent efflux pumps, inhibited by phenylalanine arginine beta-naphthylamide, expel macrolides and telithromycin in E. aerogenes.

FIG. 1.

Effect of efflux pump inhibitor on intracellular accumulation of telithromycin in E. aerogenes ATCC 13048. Exponential-phase bacteria grown in Luria-Bertani broth were removed, resuspended in sodium phosphate buffer, and incubated with radiolabeled telithromycin for various times. Intracellular telithromycin accumulation was followed in the absence (✴) or presence of PAβN at a final concentration of 5.26 (◊), 26.3 (▵), 52.6 (□), or 105.2 (○) μg/ml. Values (expressed as counts per minute/optical density) were obtained from two independent experiments carried out in duplicate.

FIG. 2.

The AcrAB-TolC efflux pump and telithromycin efflux. Exponential-phase bacteria grown in Luria-Bertani broth were removed, resuspended in sodium phosphate buffer, and incubated with radiolabeled telithromycin for various times. Intracellular telithromycin accumulation was monitored in strains EAEP289 (□, ▪), EAEP298 (○, •), and EAEP294 (▵, ▴). The experiments were carried out in the absence (open symbols) or presence (filled symbols) of PAβN (final concentration, 52.6 μg/ml). Values (expressed as counts per minute/optical density) were obtained from two independent experiments carried out in duplicate.