Carbapenemase detection in Acinetobacter baumannii clones resistant to imipenem

INTRODUCTION. The aim of this study was to detect carbapenemases in imipenem-resistant Acinetobacter baumannii isolates obtained in the microbiology department of a Basque Country Public Health Service hospital over a period of 19 months, and to genetically characterize the resistant clones. METHODS. Susceptibility tests to imipenem, meropenem, ticarcillin, ceftazidime, cefotaxime, cefepime and aztreonam were done by determining the minimum inhibitory concentration on agar plates. A tRNA technique was used for species identification and PCR with primers ERIC2, AP3 and M13 for genetic typing of resistant isolates. Carbapenemase production was detected by the Hodge test and metallo-beta-lactamase by the EDTA test and Etest MBL. RESULTS. A total of 76 isolates were resistant to imipenem and 49 of these were resistant to all the betalactam antibiotics tested. Genetic typing showed three predominant clones, denominated 1 (9 isolates), 11 (48 isolates) and Ill (8 isolates). Hodge and EDTA tests were positive in 45 and 8 isolates belonging to clone 11, 8 and 4 belonging to clone 1 and 7 and 3 belonging to clone Ill, respectively. The Etest confirmed 7 results (45% of the 17 positive EDTA test isolates). CONCLUSION. Our results show that one factor contributing to the high level of imipenem resistance in the isolates analyzed is dissemination of a predominant, multiresistant clone able to produce OXA-type carbapenemases and metallo-beta-lactamases.