• Maria Maniati, Alexandros Ikonomidis, Paraskevi Mantzana, Alexandros Daponte, Antonios N Maniatis, and Spyros Pournaras.
• Department of Microbiology, Medical School, University of Thessaly, Larissa, Greece.
• J. Antimicrob. Chemother. 2007 Jul 1; 60 (1): 132-5.

ObjectivesA 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.MethodsMICs 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.ResultsThe 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.ConclusionsMultiple carbapenem resistance mechanisms are demonstrated to coexist in a single P. aeruginosa isolate and might confer the high-level carbapenem resistance.

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