Enterobacter aerogenes, a nosocomial pathogen, is frequently exhibiting multidrug resistance mechanisms associated with a change in membrane permeability. In clinical isolates, active efflux plays a prominent role in antibiotic resistance. We report here the effect of three unrelated compounds that are able to restore a noticeable antibiotic susceptibility to resistant strains. The targeting of various parameters which contribute to the efficacy of the efflux mechanism, Such as energy, flux selectivity, or functional assembly of the membrane complex, increases the intracellular chloramphenicol concentration in resistant isolates. (C) 2002 Elsevier Science (USA). All rights reserved.