| Sumario: | Objective: Today, carbapenems are used as almost last choice for the treatment of infections with extended spectrum ?-lactamase (ESBL) producing pathogens. However, the prevalence of carbapenamase-producing strains in Enterobacteriaceae has been increasing over the last decade. In this study, carbapenem-resistant Escherichia coli and Citrobacter koseri isolates with OXA-48 carbapenemase obtained from hospitalized patients in different regions of Istanbul were investigated. Material and Methods: The strains were identified by conventional methods and VITEK 2 system. Antibiotic susceptibility test was performed using disc diffusion method, and extended-spectrum ?-lactamase production was investigated using the double-disc synergy and cefotaxime/boronic acid- cefotaxime/boronic acid/clavulanic acid tests. VITEK 2 system was used for determination of minimum inhibitory concentration (MIC) of the antibiotics. The MICs of imipenem and meropenem for the clinical isolates were also determined by E-tests. The carbapenemase production was investigated with modified Hodge test. ?-lactamase genes and plasmid mediated quinolone resistance (PMQR) determinants were screened by polymerase chain reaction (PCR). The amplification products of blaOXA-48 genes were sequenced. Conjugation experiment was used for transferring ?-lactamase gene. Results: The clinical isolates and their transconjugants were positive for blaOXA-48, however, the isolates lacked PMQR and other ?-lactamase genes such as blaTEM, blaSHV, blaCTX-M, blaVIM, blaIMP and blaKPC. The blaOXA-48 genes detected in both of the isolates were transferred to the recipient strain. The MICs were increased approximately two fold according to recipient strain in transconjugants for carbapenems. Additionally, the transconjugants conferred resistance to ampicillin, amoxicillin-clavulanic acid, piperacillin-tazobactam and cefazolin. Conclusions: The carbapenemase-producing isolates may restrict the use of these valuable antibiotics. In Turkey, the blaOXA-48 gene not only persists especially in Klebsiella pneumoniae but also it has spread among other species. The presence of OXA-48 carbapenemase in rarely encountered species should also be considered.
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