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

Abstract

AIM: To analyze the mechanisms of resistance to carbapenems among imipenem resistant A. baumannii recovered from different wards at Charles Nicolle Hospital. METHODS: 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-ß-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. RESULTS: 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 > 2048μg/ml), ticarcillin-clavulanic acid (MIC50 >1024μg/ml), aztreonam (MIC50 = 512μg/ml), ceftazidim (MIC50 = 512μg/ml), imipenem (MIC50 = 512μg/ml), meropenem (MIC50 =128μg/ml) and cefepime (MIC50 = 256μg/ml). Metallo-ß-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). CONCLUSION: 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.