title: The role of efflux pumps in macrolide resistance in Mycobacterium avium complex.
abstract: Mycobacteriumavium complex (MAC) is clinically important since it can cause severe infections in acquired immune deficiency syndrome (AIDS) patients and other immunocompromised individuals. Use of the macrolides clarithromycin and azithromycin has improved the outcome of MAC infections, but therapeutic failure is still a major problem. In this work, we studied efflux pump activity in MAC clinical strains and evaluated the contribution of active efflux to macrolide resistance. Eighteen clinical strains isolated from AIDS patients were evaluated for macrolide resistance in the presence and absence of the efflux pump inhibitors (EPIs) thioridazine, chlorpromazine and verapamil. The efflux activity of these strains was then assessed by a semi-automated fluorometric method that detects extrusion of ethidium bromide (EtBr), a known efflux pump substrate. Resistance to clarithromycin was significantly reduced in the presence of thioridazine, chlorpromazine and verapamil. The same EPIs were effective in decreasing the efflux of EtBr from MAC cells. Moreover, increased retention of [(14)C]-erythromycin in the presence of these EPIs further demonstrated that active efflux contributes to MAC resistance to macrolides. This study demonstrates that efflux pumps play an important role in MAC resistance to antibiotics.
authors.affiliation: Unit of Mycobacteriology, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa (IHMT/UNL), Lisboa, Portugal.
authors.forename: Liliana
authors.initials: L
authors.lastname: Rodrigues
authors.forename: Daniela
authors.initials: D
authors.lastname: Sampaio
authors.forename: Isabel
authors.initials: I
authors.lastname: Couto
authors.forename: Diana
authors.initials: D
authors.lastname: Machado
authors.forename: Winfried V
authors.initials: WV
authors.lastname: Kern
authors.forename: Leonard
authors.initials: L
authors.lastname: Amaral
authors.forename: Miguel
authors.initials: M
authors.lastname: Viveiros
mesh_terms: D000163:Acquired Immunodeficiency Syndrome / Q000150:complications; D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology*; D001693:Biological Transport, Active; D002746:Chlorpromazine / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D006801:Humans; D018942:Macrolides / Q000378:metabolism* / Q000494:pharmacology*; D026901:Membrane Transport Proteins / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D015269:Mycobacterium avium Complex / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism*; D015270:Mycobacterium avium-intracellulare Infection / Q000382:microbiology; D013881:Thioridazine / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D026901:Membrane Transport Proteins; D014475:Uncoupling Agents; D014700:Verapamil; D013881:Thioridazine; D002746:Chlorpromazine