Carbapenem-resistant Acinetobacter baumannii producing the carbapenemase OXA-23 in Tunisia

ABSTRACT

To analyze the mechanisms of resistance to carbapenems among imipenem resistant A. baumannii recovered from different wards at Charles Nicolle Hospital. From January to December 2007, 50 carbapenem-resistant A. baumannii isolates were recovered from hospitalized patients. MICs were performed by agar dilution method and interpreted according to CLSI guidelines. Metallo-beta-lactamase production was evaluated using imipenem-EDTA disk synergy test. PCR and DNA sequencing targeting blaOXA genes were performed and pulsed field gel electrophoresis was used for epidemiologic study. Most of the isolates were obtained from patients hospitalized in surgery [62%] and Intensive Care Units [22%]. All strains showed high level of resistance to ticarcillin [MIC50 > 2048micro g/ml], ticarcillin-clavulanic acid [MIC50 >1024micro g/ml], aztreonam [MIC50 = 512micro g/ml], ceftazidim [MIC50 = 512micro g/ml], imipenem [MIC50 = 512micro g/ml], meropenem [MIC50 =128micro g/ml] and cefepime [MIC50 = 256micro g/ml]. Metallo-beta-lactamase production was negative for all isolates. The co-existence of blaOXA-51-like/ blaOXA-23-like was detected in 82% [n= 41]. The genes blaOXA- 24-like and blaOXA-58-like were not found in any isolate. All isolates harboured a blaOXA-51-like gene. Sequencing confirmed the presence of blaOXA-23 and blaOXA-69 genes. Eight distinct patterns were observed [A 41 isolates, B 1 isolate, C 1 isolate, D 1 isolate, E 1 isolate, F 2 isolates, G 1 isolate, H 2 isolates]. Production of OXA-23 was the important mechanism of resistance to carbapenem among A. baumannii. Strengthening of prevention measures are required to control further spread of carbapenemases in Tunisia