title: Relative contributions of the AcrAB, MdfA and NorE efflux pumps to quinolone resistance in Escherichia coli.
abstract: Quinolones are widely used, broad-spectrum antimicrobial agents. In screens for genes that, when overexpressed, allow Escherichia coli to grow on otherwise lethal concentrations of the fluoroquinolone norfloxacin, the ydhE gene was identified. We have shown that ydhE encodes a multidrug efflux pump with a narrower substrate range than that of its closest homologue, encoded by norM, and named the gene norE. The relative contributions to drug resistance of NorE compared with the two other known E. coli quinolone pumps, AcrAB and MdfA, have been defined. Overexpression of each of the three pumps separately resulted in roughly similar levels of quinolone resistance, whereas simultaneous overexpression of norE or mdfA in combination with acrAB gave synergic increases in quinolone resistance. The level of quinolone resistance mediated by efflux pumps seems to be constrained to an approximately 10-fold maximum, even with increased production of the pumps. We measured the drug resistance of an isogenic set of strains containing the various permutations of single, double and triple drug efflux pump mutants. The DeltanorE and DeltamdfA mutants were somewhat more susceptible to fluoroquinolones than the parent strain, and acrAB mutants were four- to six-fold more susceptible. Mutants lacking two or all three efflux pumps were not significantly more susceptible to fluoroquinolones than those lacking only one of the three pumps.
authors.affiliation: Department of Molecular Virology and Microbiology, Mailstop BCM-280, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030-3411, USA.
authors.forename: Shirley
authors.initials: S
authors.lastname: Yang
authors.forename: Sonia Rahmati
authors.initials: SR
authors.lastname: Clayton
authors.forename: E Lynn
authors.initials: EL
authors.lastname: Zechiedrich
mesh_terms: D042462:4-Quinolones; D000890:Anti-Infective Agents / Q000494:pharmacology*; D017920:Antiporters / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D008074:Lipoproteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D018892:Proton-Motive Force
chemical_list: D042462:4-Quinolones; D000890:Anti-Infective Agents; D017920:Antiporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D008074:Lipoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D010088:Oxidoreductases; C083497:AcrA protein, E coli; C083496:AcrB protein, E coli; C118438:Mdfa protein, E coli; C114619:NorM protein, bacteria; C491958:mdtK protein, E coli; C034747:nitric-oxide reductase