A Highly Carbapenem-Resistant Pseudomonas Aeruginosa Isolate With a Novel blaVIM-4/blaP1b Integron Overexpresses Two Efflux Pumps and Lacks OprD

J Antimicrob Chemother. 2007 Jul;60(1):132-5. doi: 10.1093/jac/dkm126. Epub 2007 May 4.


Objectives: A Pseudomonas aeruginosa clinical isolate that exhibited high-level carbapenem resistance and produced metallo-beta-lactamase (MBL) was recovered from a Greek patient. This study was conducted to determine the underlying mechanisms that conferred the carbapenem resistance phenotype.

Methods: MICs were determined by Etest and Etest MBL. PCR assays were performed for identification of bla(VIM-type), other antibiotic resistance and efflux pump genes and mapping of class 1 integrons. Expression of efflux pump genes was quantified by real-time PCR. Nucleotide sequencing was used to determine the bla(VIM) allele. The location of the MBL allele was investigated by mating experiments, plasmid analysis and hybridization studies.

Results: The isolate was highly carbapenem-resistant (MICs of imipenem and meropenem were 512 and 128 mg/L, respectively) and multidrug-resistant. It harboured the beta-lactamase genes bla(VIM-4) and bla(P1b) in a novel class 1 integron named InV4P1, and a second integron with aac(6')-Ib and bla(OXA-35) gene cassettes. The isolate was deficient in porin OprD and overexpressed efflux pumps MexAB-OprM and MexXY-OprM. Conjugation experiments failed to detect transferable MBL determinants, plasmids were not visualized and bla(VIM) was detected by PCR in the chromosomal band.

Conclusions: Multiple carbapenem resistance mechanisms are demonstrated to coexist in a single P. aeruginosa isolate and might confer the high-level carbapenem resistance.

MeSH terms

  • Aged
  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Carbapenems / pharmacology*
  • Drug Resistance, Multiple, Bacterial / genetics*
  • Female
  • Greece
  • Humans
  • Integrons / genetics*
  • Microbial Sensitivity Tests
  • Porins / metabolism
  • Pseudomonas Infections / microbiology
  • Pseudomonas aeruginosa / drug effects*
  • Pseudomonas aeruginosa / enzymology
  • Pseudomonas aeruginosa / genetics
  • Pseudomonas aeruginosa / isolation & purification
  • beta-Lactam Resistance
  • beta-Lactamases / genetics*
  • beta-Lactamases / metabolism


  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Carbapenems
  • Porins
  • OprD protein, Pseudomonas aeruginosa
  • beta-Lactamases
  • beta-lactamase bla(VIM-4), Pseudomonas aeruginosa