Rapid identification of mutations in a multidrug efflux pump in Pseudomonas aeruginosa

APMIS. 1999 Dec;107(12):1109-16. doi: 10.1111/j.1699-0463.1999.tb01516.x.


The gene mexR regulates negatively the expression of the MexA-MexB-OprM efflux pump in Pseudomonas aeruginosa, and mutations in mexR cause a multiple antibiotic resistance phenotype. Five hundred and forty resistant clones of P. aeruginosa PAO503 were isolated after selection for resistance to chloramphenicol or tetracycline. All isolates showed similar phenotypes and were resistant to tetracycline, chloramphenicol and norfloxacin. Nineteen randomly selected isolates were analyzed. Since mutational analysis by direct sequencing of all regions of interest in several strains is time-consuming and expensive, a screening method, Non-Isotopic RNase Cleavage Assay (NIRCA), was applied to identify mutant genes so that they could be targeted for DNA sequencing. NIRCA is a simple but rapid method for mutational analysis and can be performed in 3-4 h. Results of NIRCA analysis were compared with DNA sequencing. Both NIRCA and DNA sequencing analysis showed mexR gene mutations in 11 of 19 isolates but no alterations in 8 strains. An immunoblot assay showed overexpression of OprN, a component of another multidrug efflux pump, MexE-MexF-OprN, in those eight isolates. Nucleotide sequencing of quinolone resistance-determining regions of DNA gyrase (gyrA) or topoisomerase IV (parC) showed no alterations in any of the 19 mutants. The data indicate that two efflux pump systems, MexA-MexB-OprM and MexE-MexF-OprN, were involved in multidrug resistance including quinolones and that NIRCA is a sensitive method for screening mutations.

Publication types

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

MeSH terms

  • Bacterial Outer Membrane Proteins / genetics*
  • Base Sequence
  • Carrier Proteins / genetics*
  • DNA Mutational Analysis
  • DNA Primers / genetics
  • Drug Resistance, Multiple / genetics
  • Genes, Bacterial
  • Genes, Regulator
  • Humans
  • Membrane Transport Proteins*
  • Mutation*
  • Pseudomonas aeruginosa / drug effects
  • Pseudomonas aeruginosa / genetics*
  • Pseudomonas aeruginosa / metabolism
  • Ribonucleases


  • Bacterial Outer Membrane Proteins
  • Carrier Proteins
  • DNA Primers
  • Membrane Transport Proteins
  • MexA protein, Pseudomonas aeruginosa
  • MexB protein, Pseudomonas aeruginosa
  • OprM protein, Pseudomonas aeruginosa
  • OprN protein, Pseudomonas aeruginosa
  • Ribonucleases