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 Influence of the MexA-MexB-oprM multidrug efflux system on expression of the MexC-MexD-oprJ and MexE-MexF-oprN multidrug efflux systems in Pseudomonas aeruginosa. [J Antimicrob Chemother. 2000] PMID:11102405 Overexpression of the multidrug efflux pumps MexCD-OprJ and MexEF-OprN is associated with a reduction of type III secretion in Pseudomonas aeruginosa. [J Bacteriol. 2005] PMID:15687203 Clinical strains of Pseudomonas aeruginosa overproducing MexAB-OprM and MexXY efflux pumps simultaneously. [Antimicrob Agents Chemother. 2004] PMID:15105137 Expression of Pseudomonas aeruginosa multidrug efflux pumps MexA-MexB-OprM and MexC-MexD-OprJ in a multidrug-sensitive Escherichia coli strain. [Antimicrob Agents Chemother. 1998] PMID:9449262 Efflux-mediated resistance to tigecycline (GAR-936) in Pseudomonas aeruginosa PAO1. [Antimicrob Agents Chemother. 2003] PMID:12604529