Sequential outbreaks of multidrug-resistant Acinetobacter baumannii in intensive care units of a tertiary referral hospital in Italy: combined molecular approach for epidemiological investigation

SummaryA laboratory-based surveillance study was conducted from January 2007 to May 2010 in San Martino Tertiary Referral Hospital in Genoa, Italy in which the molecular epidemiology of multidrug-resistant Acinetobacter baumannii was investigated in the five intensive care units (ICUs). A total of 53 A. baumannii strains were isolated from patients admitted to ICUs (69.8%) and to other epidemiologically linked hospital wards (30.2%) and were genotyped by repetitive extragenic palindromic polymerase chain reaction (REP-PCR), multilocus sequence typing (MLST) and adeB sequence typing. REP-PCR fingerprinting analysis, MLST and adeB typing results were well correlated and allowed us to classify strains causing epidemic events into three major epidemic clones: A (REP-I/ST4, adeB-STII genotype) isolated for the first time in May 2007, B (REP-IV/ST95, adeB-STI genotype) from November 2007 to May 2009 and C (REP-VII/ST118, adeB-STII genotype) from July 2008 to May 2010. MLST results demonstrated that epidemic clones A and C were related as they were members of the widespread clonal complex CC92. The genetic determinants of carbapenem resistance were investigated and resistance associated with the presence of the blaOxA-58-like gene with ISAba2 and ISAba3 elements flanking it in clone A, and with the blaOxA-23-like gene flanked by ISAba1 in clones B and C. A molecular approach allowed the prompt introduction of infection control measures and the evaluation of data in a global epidemiological context.