Epidemiology and clonality of carbapenem-resistant Acinetobacter baumannii from an intensive care unit in Palermo, Italy

BACKGROUND: Multidrug-resistant Acinetobacter baumannii, initially considered as having a poor clinical relevance, is frequently isolated from infection cases in intensive care units. We describe the epidemiology of carbapenem resistant A. baumannii (CRAB) in a general ICU in Palermo, Italy, from October 2010 to March 2011. FINDINGS: 58 of 61 isolates exhibited MICs for meropenem or imipenem ≥16 mg/L. Forty-nine carried bla(OXA-23) and two bla(OXA-58) genes. Five subtype clusters were detected by rep-PCR. Clusters D and E included 10 isolates that tested negative for the carbapenem resistance genes. MLST attributed all isolates, but two, with sequence type (ST)2, whereas the two remaining isolates with ST78. The respiratory tract was the most common site of infection (26 out of 36 cases. 72.2%). A high infection related mortality rate was observed (18 out of 35 patients, 51.4%). Nineteen patients tested positive for other multidrug resistant organisms in addition to CRAB. In eight cases isolates belonging to distinct subtype clusters and/or with distinct carbapenemase profiles were identified. CONCLUSIONS: Carbapenem resistance was prominently driven by the dissemination of CRAB isolates belonging to ST2, carrying the carbapenemase gene bla(OXA-23). The colonization/infection of some patients by multiple strains is suggestive of an endemic circulation of CRAB.