title: Contributions of MexAB-OprM and an EmrE homolog to intrinsic resistance of Pseudomonas aeruginosa to aminoglycosides and dyes.
abstract: Of the six putative small multidrug resistance (SMR) family proteins of Pseudomonas aeruginosa, a protein encoded by the PA4990 gene (emrE(Pae)) shows the highest identity to the well-characterized EmrE efflux transporter of Escherichia coli. Reverse transcription-PCR confirmed the expression of emrE(Pae) in the wild-type strain of P. aeruginosa. Using isogenic emrE(Pae), 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 EmrE(Pae) 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.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3206, USA.
authors.forename: Xian-Zhi
authors.initials: XZ
authors.lastname: Li
authors.forename: Keith
authors.initials: K
authors.lastname: Poole
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nikaido
mesh_terms: D000595:Amino Acid Sequence; D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017920:Antiporters / Q000187:drug effects / Q000235:genetics*; D001425:Bacterial Outer Membrane Proteins / Q000187:drug effects / Q000235:genetics*; D002352:Carrier Proteins / Q000187:drug effects / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D029968:Escherichia coli Proteins; D008565:Membrane Proteins / Q000187:drug effects / Q000235:genetics*; D026901:Membrane Transport Proteins; D008826:Microbial Sensitivity Tests; D010957:Plasmids; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics*
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D017920:Antiporters; D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C118598:MexA protein, Pseudomonas aeruginosa; C075436:EmrE protein, E coli