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Antimicrobial Agents and Chemotherapy, December 2007, p. 4329-4335, Vol. 51, No. 12
0066-4804/07/$08.00+0     doi:10.1128/AAC.00810-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Molecular Epidemiology and Mechanisms of Carbapenem Resistance in Pseudomonas aeruginosa Isolates from Spanish Hospitals

Servicio de Microbiología and Unidad de Investigación, Hospital Son Dureta, Instituto Universitario de Investigación en Ciencias de la Salud (IUNICS), Palma de Mallorca,¹ Servicio de Microbiología, Hospital General Universitario Gregorio Marañón, Madrid,² Servicio de Microbiología, Hospital de la Santa Creu i Sant Pau, and Departament de Genètica i Microbiologia, Universidad Autònoma de Barcelona, Barcelona, Spain³

Received 22 June 2007/ Returned for modification 30 August 2007/ Accepted 3 October 2007

All (236) Pseudomonas aeruginosa isolates resistant to imipenem and/or meropenem collected during a multicenter (127-hospital) study in Spain were analyzed. Carbapenem-resistant isolates were found to be more frequently resistant to all ß-lactams and non-ß-lactam antibiotics than carbapenem-susceptible isolates (P < 0.001), and up to 46% of the carbapenem-resistant isolates met the criteria used to define multidrug resistance (MDR). Pulsed-field gel electrophoresis revealed remarkable clonal diversity (165 different clones were identified), and with few exceptions, the levels of intra- and interhospital dissemination of clones were found to be low. Carbapenem resistance was driven mainly by the mutational inactivation of OprD, accompanied or not by the hyperexpression of AmpC or MexAB-OprM. Class B carbapenemases (metallo-ß-lactamases [MBLs]) were detected in a single isolate, although interestingly, this isolate belonged to one of the few epidemic clones documented. The MBL-encoding gene (bla_VIM-2), along with the aminoglycoside resistance determinants, was transferred to strain PAO1 by electroporation, demonstrating its plasmid location. The class 1 integron harboring bla_VIM-2 was characterized as well, and two interesting features were revealed: intI1 was found to be disrupted by a 1.1-kb insertion sequence, and a previously undescribed aminoglycoside acetyltransferase-encoding gene [designated aac(6')-32] preceded bla_VIM-2. AAC(6')-32 showed 80% identity to AAC(6')-Ib' and the recently described AAC(6')-31, and when aac(6')-32 was cloned into Escherichia coli, it conferred resistance to tobramycin and reduced susceptibility to gentamicin and amikacin. Despite the currently low prevalence of epidemic clones with MDR, active surveillance is needed to detect and prevent the dissemination of these clones, particularly those producing integron- and plasmid-encoded MBLs, given their additional capacity for the intra- and interspecies spread of MDR.

Published ahead of print on 15 October 2007.

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