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

https://doi.org/10.1016/j.ijantimicag.2017.01.028Get rights and content

Highlights

  • 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%.

Abstract

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.

Introduction

Acinetobacter baumannii isolates are increasingly causing severe infections among debilitated patients, particularly in intensive care units (ICUs) [1]. Carbapenem resistance is currently widespread among A. baumannii, with rates reaching or exceeding 90% in Southern and Eastern European countries [2]. Carbapenem-resistant A. baumannii (CRAB) are commonly resistant to most available antimicrobials except colistin, tigecycline and minocycline [3], [4]. Tracking the evolution and clonal composition of CRAB isolates is important to support the implementation of control strategies. Molecular epidemiological studies usually reveal clonality of CRAB, with outbreak strains usually belonging to international clones (IC) 1 and 2 and a few additional clonal lineages [5].

In Greek hospitals, during the last few years the vast majority of A. baumannii isolates are CRAB [2], which currently represent the most frequent infection pathogen in the ICU (http://www.mednet.gr/whonet/). Regarding their clonal nature and carbapenemase gene content, we showed previously in a Greek nationwide study conducted from 2000 to 2009 that CRAB were harbouring only the OXA-58 carbapenemase gene; IC1 was the most common lineage until 2004, with IC2 prevailing during 2005–2009 [6].

Studies in several European countries have shown that OXA-23 tends to gradually replace OXA-58 among CRAB [7], [8]. Also, a preliminary study from a single Greek hospital in 2011 reported that OXA-23 was more common than OXA-58 [9]. Given the increased frequency and importance of CRAB, the present follow-up nationwide study was conducted to analyse the resistance phenotypes, carbapenemase gene content, genetic relatedness and evolution of clonal lineages among CRAB recovered from Greek patients during 2015.

Section snippets

Bacterial strains

During 2015, as many as 2500 A. baumannii isolates were identified in 11 tertiary hospitals located in eight cities in Northern (Thessaloniki, Serres, Alexandroupolis), Western (Ioannina), Central (Athens, Piraeus, Larissa) and Southern (Heraklion) Greece. The rate of CRAB in these hospitals during 2015 was 95%, with virtually all clinically important A. baumannii being CRAB. The present study included 194 randomly selected non-repetitive CRAB isolates recovered during 2015 from clinical

Patient data, susceptibility testing and carbapenemase genes

Of the patients that yielded CRAB, 70.1% were male and 29.9% female; most of them were hospitalised in ICUs (56.2%), 20.6% in medical wards, 17% in surgical wards, 2.1% in long-term care facilities and 4.1% were outpatients. Isolates were obtained from blood (45.9%), the respiratory tract (21.6%), skin and soft tissue (11.3%), urine (9.3%) and various other clinical samples (11.9%).

The 194 CRAB isolates showed imipenem and meropenem MICs ≥ 32 µg/mL and were non-susceptible to all

Discussion

Acinetobacter baumannii exhibits particularly high carbapenem resistance rates in several regions worldwide [22]. Of note, during 2015 essentially no clinically important carbapenem-susceptible A. baumannii isolate has been recovered in the study Greek hospitals. The almost universal resistance to carbapenems and SAM precludes the use of β-lactams and considerably limits effective treatment options. Carbapenem resistance in A. baumannii is regularly due to the production of oxacillinases, the

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