1: J Antimicrob Chemother. 2007 Mar;59(3):378-86. Epub 2007 Feb 8.

A combined phenotypic and genotypic method for the detection of Mex efflux pumps 
in Pseudomonas aeruginosa.

Mesaros N, Glupczynski Y, Avrain L, Caceres NE, Tulkens PM, Van Bambeke F.

Unité de Pharmacologie cellulaire et moléculaire, Brussels, Université catholique
de Louvain, UCL 7370 avenue E. Mounier 73, B-1200 Bruxelles, Belgium.

BACKGROUND: Mex efflux pumps contribute to multidrug resistance in Pseudomonas
aeruginosa. Evidencing their expression in clinical isolates would help in
rationalizing antibiotic selection. METHODS: We have developed a combined
phenotypic and genotypic approach for the differential diagnosis of resistance
mediated by four major transporters (MexAB-OprM, MexCD-OprJ, MexEF-OprN,
MexXY-OprM). The methodology was validated using reference strains harbouring
only one specific transporter and its applicability evaluated towards seven
selected clinical isolates, the resistance mechanisms of which could not be
assigned by conventional techniques. Phenotypic detection used MIC measurements
with reporter antibiotics [carbenicillin (MexAB-OprM); erythromycin (MexCD-OprJ);
norfloxacin and imipenem (MexEF-OprN); gentamicin (MexXY-OprM)] with and without 
Phe-Arg-beta-naphthylamide. Genotypic detection was made by semi-quantitative
reverse transcription PCR (RT-PCR) for mexC and mexE, and by quantitative
competitive RT-PCR and real-time PCR for mexA and mexX (correlation between both 
methods: > 88 % ; overexpression levels ranging between 4.8 and 8.1). RESULTS:
Convergence between phenotypic and genotypic methods was observed in control
strains for all pumps. For clinical isolates, convergence was obtained in 6 of 7 
strains for MexXY-OprM and MexEF-OprM, and in 5 of 7 for MexAB-OprM and
MexCD-OprJ, mostly due to hard to interpret phenotypic data. CONCLUSIONS: The
data plead for combining phenotypic and genotypic approaches in the diagnosis of 
efflux-mediated resistance in P. aeruginosa.

PMID: 17289770 [PubMed - indexed for MEDLINE]

Related Links

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MexC-MexD-oprJ and MexE-MexF-oprN multidrug efflux systems in Pseudomonas
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    Overexpression of the multidrug efflux pumps MexCD-OprJ and MexEF-OprN is
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