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Antimicrobial Agents and Chemotherapy, January 2003, p. 27-33, Vol. 47, No. 1
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.1.27-33.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Contributions of MexAB-OprM and an EmrE Homolog to Intrinsic Resistance of Pseudomonas aeruginosa to Aminoglycosides and Dyes

Xian-Zhi Li,1 Keith Poole,2 and Hiroshi Nikaido1*

Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3206,1 Department of Microbiology and Immunology, Queen's University, Kingston, Ontario K7L 3N6, Canada2

Received 9 July 2002/ Returned for modification 9 September 2002/ Accepted 24 September 2002

Of the six putative small multidrug resistance (SMR) family proteins of Pseudomonas aeruginosa, a protein encoded by the PA4990 gene (emrEPae) shows the highest identity to the well-characterized EmrE efflux transporter of Escherichia coli. Reverse transcription-PCR confirmed the expression of emrEPae in the wild-type strain of P. aeruginosa. Using isogenic emrEPae, mexAB-oprM, and/or mexB deletion mutants, the contributions of the EmrE protein and the MexAB-OprM efflux system to drug resistance in P. aeruginosa were assessed by a drug susceptibility test carried out in a low-ionic-strength medium, Difco nutrient broth. We found that EmrEPae contributed to intrinsic resistance not only to ethidium bromide and acriflavine but also to aminoglycosides. In this low-ionic-strength medium, MexAB-OprM was also shown to contribute to aminoglycoside resistance, presumably via active efflux. Aminoglycoside resistance caused by these two pumps could not be demonstrated in high-ionic-strength media, such as Luria broth or Mueller-Hinton broth. The EmrE-dependent efflux of ethidium bromide was confirmed by a continuous fluorescence assay.

* Corresponding author. Mailing address: Department of Molecular and Cell Biology, 426 Barker Hall, University of California, Berkeley, CA 94720-3202. Phone: (510) 642-2027. E-mail: nhiroshi{at}uclink4.berkeley.edu.

Antimicrobial Agents and Chemotherapy, January 2003, p. 27-33, Vol. 47, No. 1
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.1.27-33.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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