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Antimicrobial Agents and Chemotherapy, May 2004, p. 1676-1680, Vol. 48, No. 5
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.5.1676-1680.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Role of the Multidrug Efflux System MexXY in the Emergence of Moderate Resistance to Aminoglycosides among Pseudomonas aeruginosa Isolates from Patients with Cystic Fibrosis

Christelle Vogne,1 Julio Ramos Aires,2 Christiane Bailly,1 Didier Hocquet,1 and Patrick Plésiat1*

Laboratoire de Bactériologie, Hôpital Jean Minjoz, F-25030 Besançon, France,1 Department of Molecular and Cell Biology, University of California, Berkeley, California 947202

Received 6 August 2003/ Returned for modification 31 October 2003/ Accepted 23 January 2004

This study investigates the role of active efflux system MexXY in the emergence of aminoglycoside (AG) resistance among cystic fibrosis (CF) isolates of Pseudomonas aeruginosa. Three genotypically related susceptible and resistant (S/R) bacterial pairs and three other AG-resistant CF strains were compared to four non-CF strains moderately resistant to AGs. As demonstrated by immunoblot experiments, pump MexY was strongly overproduced in all of the resistant bacteria. This MexXY upregulation was associated with a 2- to 16-fold increase in the MICs of AGs in the S/R pairs and lower intracellular accumulation of dihydrostreptomycin. Alterations in mexZ, the repressor gene of operon mexXY, were found in all of the AG-resistant CF isolates and in one non-CF strain. Complementation of these bacteria with a plasmid-borne mexZ gene dramatically reduced the MICs of AGs, thus highlighting the role played by MexXY in the development of moderate resistance in CF patients. In contrast, complementation of the three non-CF strains showing wild-type mexZ genes left residual levels of resistance to AGs. These data indicate that a locus different from mexZ may be involved in overproduction of MexXY and that other nonenzymatic mechanisms contribute to AG resistance in P. aeruginosa.

* Corresponding author. Mailing address: Laboratoire de Bactériologie, Hôpital Jean Minjoz, 25030 Besançon Cedex, France. Phone: (33) 3-81-66-82-86. Fax: (33) 3-81-66-89-14. E-mail: patrick.plesiat{at}univ-fcomte.fr.

Antimicrobial Agents and Chemotherapy, May 2004, p. 1676-1680, Vol. 48, No. 5
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.5.1676-1680.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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