Predominance of international clone 2 OXA-23-producing-Acinetobacter baumannii clinical isolates in Greece, 2015: results of a nationwide studyâ˜

- Greece has the highest rate of carbapenem-resistant A. baumannii (CRAB) in Europe.
- Of the 194 CRAB isolates tested, the vast majority (98.5%) produced OXA-23 carbapenemase.
- Colistin showed an alarming resistance rate (27.3%) followed by minocycline (28.4%).
- Cotrimoxazole exhibited susceptibility rates of 34.6%.
- Of 194 isolates throughout Greece, IC2 comprised 80.9% and IC1 18.6%.

In a previous nationwide study in Greece, OXA-58 was the sole carbapenemase present among carbapenem-resistant Acinetobacter baumannii (CRAB) isolated between 2000 and 2009. In this study, the antibiotic resistances, carbapenemase gene content and clonal relatedness of 194 single-patient CRAB clinical isolates collected randomly during 2015 from 11 tertiary hospitals located throughout Greece were investigated. Antimicrobial susceptibility was determined using commercial and dilution methods. PCR assays for carbapenemase genes were performed. Clonality was tested by a scheme based on two multiplex PCRs and single-locus blaOXA-51-like sequence-based typing. Furthermore, Pasteur's multilocus sequence typing (MLST) scheme and pulsed-field gel electrophoresis (PFGE) were applied to 31 selected representative isolates. The most active antibiotics were trimethoprim/sulfamethoxazole (SXT) (34.6% of isolates susceptible), minocycline (71.6%), colistin (72.7%) and tigecycline (MIC50/90 values, 1/2 mg/L). The blaOXA-23-like gene was identified in 188 isolates (96.9%), blaOXA-23-like together with blaOXA-58-like in 3 isolates (1.5%), blaOXA-58-like in 2 isolates (1.0%) and blaOXA-40-like in 1 isolate (0.5%). ISAba1 was found upstream of the blaOXA-23-like gene in all isolates. International clone (IC) 2 comprised 157 isolates (80.9%), IC1 comprised 36 isolates (18.6%) and ST78 comprised 1 isolate (0.5%). All IC2 and IC1 isolates tested by MLST were ST2 and ST1, respectively. Seven PFGE types were detected. IC2 isolates were resistant to more antibiotics than IC1, except for SXT. This nationwide study showed that CRAB isolates in Greek hospitals currently produce almost uniformly the OXA-23 carbapenemase and belong mainly to IC2 and, to a lesser extent, IC1. Of particular concern, colistin susceptibility is recently severely reduced.