[The presence of OXA type carbapenemases in Pseudomonas strains: first report from Turkey]

Pseudomonas spp. that are one of the important nosocomial pathogens worldwide, and carbapenem resistance is observed in an increasing rate. Major factors leading to carbapenem resistance are metallo-beta-lactamases (MBLs) and carbapenem-hydrolyzing class D oxacillinases. MBLs are frequently prevalent in Pseudomonas spp., while carbapenem-hydrolyzing class D oxacillinases has been almost exclusively found in multidrug and carbapenem-resistant Acinetobacter baumannii. The aim of this study was to investigate the presence of OXA-23, OXA-40 and OXA-58 genes that encode carbapenemases, in carbapenem-resistant Pseudomonas spp. strains. A total of 184 imipenem and/or meropenem-resistant Pseudomonas spp. strains isolated from different clinical samples (85 bronchoalveolar lavage, 31 wound, 18 tracheal aspirate, 16 urine, 14 blood, 10 sputum, 3 catheter, 3 throat, 2 drainage fluid, 1 abscess, 1 peritoneal fluid) in Medical Microbiology Laboratory of Necmettin Erbakan University Meram Faculty of Medicine, between November 2011 to October 2013, were included in the study. The isolates were identified by conventional methods and an automated system (VITEK-2 Compact, bioMerieux, France), while the antibiotic susceptibility tests were performed with Kirby-Bauer disk diffusion method and automated system according to the recommendations of CLSI. The presence of OXA-23, OXA-40 and OXA-58 genes in strains were investigated by a commercial PCR kit (Hyplex CarbOxa ID; Amplex Diagnostics GmbH, Germany). Molecular studies were carried out in three steps, namely extraction of genomic DNA; multiplex PCR amplification and hybridization. In the final step, hybridization was achieved in the ELISA-based system. In our study, 12 (6.5%) out of 184 carbapenem-resistant Pseudomonas spp. strains were positive for OXA-23, 1 (0.54%) for OXA-40 and 1 (0.54%) for OXA-58, with a total positive rate of 7.6% (n= 14). Most of the carbapenem-resistant Pseudomonas spp. strains (129/184; 70%) were isolated from the samples of patients in intensive-care units, and bronchoalveolar lavage specimens were the most prevalent samples (85/184; 46.2%). This study determined the presence and frequency of OXA type carbapenemases among Pseudomonas strains for the first time in our region and Turkey. These resistance genes demonstrated in Acinetobacter spp. were also detected in this study in Pseudomonas spp. and they may cause carbapenem resistance directly or by affecting the other resistance mechanisms with a synergistic effect. This study is expected to provide a basis for further studies to elucidate resistance mechanisms.