Evolution of multidrug-resistant Acinetobacter baumannii clonal lineages: a 10 year study in Greece (2000-09)

Objectives: To analyse the evolution and genetic relatedness of Acinetobacter baumannii clonal lineages in Greece during a 10 year period. Methods: The study included 94 randomly selected A. baumannii clinical isolates recovered from 2000 to 2009 in eight tertiary Greek hospitals. Carbapenem MICs were determined by agar dilution. PCR was applied for carbapenemase genes. Isolates were typed by PFGE and tri-locus sequence typing (3LST), and 25 were also typed by multilocus sequence typing (MLST) developed by the Institut Pasteur, followed by e-Burst analysis. Results: All isolates were multidrug-resistant (MDR); 54 (57.4%) were non-susceptible to imipenem and/or meropenem. The bla(OXA-58) gene was identified in 51 (94.4%) carbapenem-non-susceptible and 15 (37.5%) carbapenem-susceptible isolates; other carbapenemase genes were not detected. Eight different PFGE types were identified. Sequence typing revealed previously characterized 3LST groups (1, 2, 4 and 5) and MLST types (STs) (1, 2, 15, 45 and 54) and the novel STs 85 (in two distant hospitals) and 86. Eight novel 3LST alleles were identified. Fifty-two (55.3%) isolates were assigned to 3LST group 1 and ST2 or ST45, both corresponding to international clonal complex 2 (CC2). Thirty-one (33.0%) isolates were assigned to 3LST group 2 and ST1 (CC1). From 2000 to 2004 63% of isolates belonged to 3LST group 2, but from 2005 to 2009 87.5% of isolates belonged to 3LST group 1; this shift was accompanied by an increase in carbapenem resistance from 43.5% to 64.6% of isolates. Conclusions: The emergence of MDR A. baumannii in Greece was associated with CC1 and CC2, which are disseminated worldwide, often harbouring the bla(OXA-58) gene. Novel 3LST alleles and STs were also detected, underlining an evolutionary divergence in Greece.