Relative contributions of the AcrAB, MdfA and NorE efflux pumps to quinolone resistance in Escherichia coli

J Antimicrob Chemother. 2003 Mar;51(3):545-56. doi: 10.1093/jac/dkg126.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 4-Quinolones
  • Anti-Infective Agents / pharmacology*
  • Antiporters / biosynthesis
  • Antiporters / genetics
  • Antiporters / physiology
  • Bacterial Proteins / biosynthesis
  • Bacterial Proteins / genetics
  • Bacterial Proteins / physiology*
  • Carrier Proteins / biosynthesis
  • Carrier Proteins / genetics
  • Carrier Proteins / physiology*
  • Drug Resistance, Bacterial* / genetics
  • Escherichia coli / drug effects*
  • Escherichia coli / enzymology
  • Escherichia coli / genetics
  • Escherichia coli Proteins / biosynthesis
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / physiology*
  • Gene Expression Regulation, Bacterial
  • Lipoproteins / biosynthesis
  • Lipoproteins / genetics
  • Lipoproteins / physiology*
  • Membrane Proteins / biosynthesis
  • Membrane Proteins / genetics
  • Membrane Proteins / physiology*
  • Membrane Transport Proteins / biosynthesis
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / physiology*
  • Multidrug Resistance-Associated Proteins
  • Oxidoreductases / biosynthesis
  • Oxidoreductases / genetics
  • Oxidoreductases / physiology*
  • Proton-Motive Force


  • 4-Quinolones
  • AcrA protein, E coli
  • AcrB protein, E coli
  • Anti-Infective Agents
  • Antiporters
  • Bacterial Proteins
  • Carrier Proteins
  • Escherichia coli Proteins
  • Lipoproteins
  • Mdfa protein, E coli
  • Membrane Proteins
  • Membrane Transport Proteins
  • Multidrug Resistance-Associated Proteins
  • NorM protein, bacteria
  • mdtK protein, E coli
  • Oxidoreductases
  • nitric-oxide reductase