title: Wide dissemination of linezolid-resistant Staphylococcus epidermidis in Greece is associated with a linezolid-dependent ST22 clone.
abstract: OBJECTIVE
  Dependence on linezolid was recently described as significant growth acceleration of linezolid-resistant Staphylococcus epidermidis (LRSE) isolates upon linezolid exposure. We investigated the possible contribution of linezolid dependence to LRSE dissemination in Greece.
  
  
  METHODS
  Linezolid resistance rates were estimated in six tertiary hospitals located throughout Greece between 2011 and 2013. Sixty-three randomly selected LRSE recovered in these hospitals during this period were studied. Growth curve analysis was conducted with and without linezolid. Clonality of the isolates was investigated by PFGE and MLST.
  
  
  RESULTS
  During the study period, the LRSE rate in the participating hospitals rose significantly from 6.9% to 9% (P = 0.006); the increase was more prominent in ICUs (from 15.1% to 20.9%; P = 0.005). Forty-seven (74.6%) of the 63 LRSE, derived from all study hospitals, clearly exhibited linezolid dependence, growing significantly faster in the presence of 16 and 32 mg/L linezolid. Of note, 61 (96.8%) LRSE exhibited a single macrorestriction pattern and belonged to ST22, which included all linezolid-dependent LRSE. The remaining two LRSE belonged to unique STs. Five of six linezolid-dependent isolates tested also exhibited linezolid dependence upon exposure to 8 mg/L linezolid. Interestingly, five of six ST22 linezolid-non-dependent isolates tested developed linezolid dependence when linezolid exposure preceded growth analysis.
  
  
  CONCLUSIONS
  The rapid LRSE dissemination in Greek hospitals threatens linezolid activity. The observation that most LRSE belonged to ST22 and expressed dependence on linezolid clearly implies that the spread of linezolid resistance should have been driven by this trait, which provided the LRSE with a selective advantage under linezolid pressure.
authors.affiliation: Department of Hygiene and Epidemiology, Medical School, University of Thessaly, Larissa, Greece.
authors.forename: Vasilios
authors.initials: V
authors.lastname: Karavasilis
authors.affiliation: Department of Microbiology, Tzaneio Hospital, Piraeus, Greece.
authors.forename: Olympia
authors.initials: O
authors.lastname: Zarkotou
authors.affiliation: Department of Microbiology, Medical School, University of Thrace, Alexandroupolis, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Panopoulou
authors.affiliation: Department of Microbiology, Medical School, Aristotelian University of Thessaloniki, Thesaloniki, Greece.
authors.forename: Melina
authors.initials: M
authors.lastname: Kachrimanidou
authors.affiliation: Department of Microbiology, Tzaneio Hospital, Piraeus, Greece.
authors.forename: Katerina
authors.initials: K
authors.lastname: Themeli-Digalaki
authors.affiliation: Department of Microbiology, KAT Hospital, Athens, Greece.
authors.forename: Antonios
authors.initials: A
authors.lastname: Stylianakis
authors.affiliation: Department of Microbiology, Medical School, University of Athens, Athens, Greece.
authors.forename: Vassiliki
authors.initials: V
authors.lastname: Gennimata
authors.affiliation: Department of Hygiene and Epidemiology, Medical School, University of Thessaly, Larissa, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Ntokou
authors.affiliation: Department of Biochemistry, Medical School, University of Patras, Patras, Greece.
authors.forename: Constantinos
authors.initials: C
authors.lastname: Stathopoulos
authors.affiliation: Department of Microbiology, Medical School, University of Athens, Athens, Greece.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Tsakris
authors.affiliation: Department of Microbiology, Medical School, University of Athens, Athens, Greece spournaras@med.uoa.gr.
authors.forename: Spyros
authors.initials: S
authors.lastname: Pournaras
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D005838:Genotype; D006115:Greece / Q000453:epidemiology; D006801:Humans; D000069349:Linezolid / Q000378:metabolism / Q000494:pharmacology*; D058885:Multilocus Sequence Typing; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology*; D013212:Staphylococcus epidermidis / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development*; D062606:Tertiary Care Centers
chemical_list: D000900:Anti-Bacterial Agents; D000069349:Linezolid
keywords: MLST; growth curves; linezolid dependence; linezolid pressure; linezolid resistance