Detection of an IS21 insertion sequence in the mexR gene of Pseudomonas aeruginosa increasing beta-lactam resistance

FEMS Microbiol Lett. 2004 Jan 15;230(1):143-6. doi: 10.1016/S0378-1097(03)00882-6.


To understand the regulation of the MexAB OprM efflux system in a clinical strain of Pseudomonas aeruginosa presenting a decreased susceptibility to ticarcillin and aztreonam, the mexR repressor gene was amplified by polymerase chain reaction (PCR) and was shown to be disrupted by an insertion sequence of more than 2 kb, with characteristic direct and inverted repeat sequences. Sequencing revealed a 2131-bp IS21 insertion sequence. A reverse transcription PCR method was used to quantify mexA transcripts and showed an increased transcription rate of mexA in this strain, compared with a PAO1 control strain. The nalB phenotype in P. aeruginosa may be due to point mutations, but also to the presence of an insertion sequence in the mexR regulator gene.

MeSH terms

  • Bacterial Outer Membrane Proteins / genetics
  • Bacterial Outer Membrane Proteins / metabolism
  • Bacterial Proteins*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • DNA Transposable Elements / genetics*
  • Gene Expression Regulation, Bacterial*
  • Humans
  • Infant
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism
  • Microbial Sensitivity Tests
  • Operon
  • Polymerase Chain Reaction / methods
  • Pseudomonas aeruginosa / drug effects*
  • Repressor Proteins / genetics*
  • Repressor Proteins / metabolism
  • Transcription, Genetic
  • beta-Lactam Resistance / genetics*
  • beta-Lactams / pharmacology


  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • Carrier Proteins
  • DNA Transposable Elements
  • Membrane Transport Proteins
  • MexA protein, Pseudomonas aeruginosa
  • MexB protein, Pseudomonas aeruginosa
  • MexR protein, Pseudomonas aeruginosa
  • OprM protein, Pseudomonas aeruginosa
  • Repressor Proteins
  • beta-Lactams