title: Increased frequency of linezolid resistance among clinical Enterococcus faecium isolates from German hospital patients.
abstract: Linezolid is an antibiotic of last resort for the treatment of infections with vancomycin-resistant enterococci (VRE). Here we report the increasing prevalence of linezolid resistance among clinical Enterococcus faecium strains from German hospital patients. Linezolid minimum inhibitory concentrations (MICs) were determined for 4461 clinical E. faecium strains isolated between 2008 and 2014. Isolates originated from the network of diagnostic laboratories collaborating with the National Reference Centre (NRC) for Staphylococci and Enterococci covering all German federal states. All linezolid-resistant isolates were determined by broth microdilution and confirmed by Etest as well as by analysing the 23S rDNA for putative mutations. Marker genes were determined by PCR. Genotyping was performed by SmaI macrorestriction analysis in pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) for selected isolates. An increase in linezolid resistance was observed, from <1% in 2008 to >9% in 2014. Occasionally, outbreaks with linezolid-resistant VRE (ST117) were observed. In total, 232 (92.4%) of 251 linezolid-resistant E. faecium isolates (including 61 vanA and 29 vanB) contained the G2576T 23S rDNA mutation and showed a varying mixture of wild-type and mutated alleles per genome sufficient to confer linezolid resistance. In vitro growth experiments revealed a stable linezolid MIC. Of the 251 linezolid-resistant isolates, 5 were cfr-positive. In conclusion, these NRC data identified a country-wide ongoing trend of increasing linezolid resistance among clinical E. faecium isolates within the last 5 years.
authors.affiliation: National Reference Centre (NRC) for Staphylococci and Enterococci, Division of Nosocomial Pathogens and Antibiotic Resistances, Department of Infectious Diseases, Robert Koch Institute, Wernigerode Branch, Burgstraße 37, D-38855 Wernigerode, Germany.
authors.forename: Ingo
authors.initials: I
authors.lastname: Klare
authors.affiliation: National Reference Centre (NRC) for Staphylococci and Enterococci, Division of Nosocomial Pathogens and Antibiotic Resistances, Department of Infectious Diseases, Robert Koch Institute, Wernigerode Branch, Burgstraße 37, D-38855 Wernigerode, Germany.
authors.forename: Carola
authors.initials: C
authors.lastname: Fleige
authors.affiliation: National Reference Centre (NRC) for Staphylococci and Enterococci, Division of Nosocomial Pathogens and Antibiotic Resistances, Department of Infectious Diseases, Robert Koch Institute, Wernigerode Branch, Burgstraße 37, D-38855 Wernigerode, Germany.
authors.forename: Uta
authors.initials: U
authors.lastname: Geringer
authors.affiliation: Faculty of Medicine Carl Gustav Carus, Technische Universität Dresden, Fiedlerstraße 42, D-01307 Dresden, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Thürmer
authors.affiliation: National Reference Centre (NRC) for Staphylococci and Enterococci, Division of Nosocomial Pathogens and Antibiotic Resistances, Department of Infectious Diseases, Robert Koch Institute, Wernigerode Branch, Burgstraße 37, D-38855 Wernigerode, Germany.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Bender
authors.affiliation: Heidelberg University Hospital, Department of Infectious Diseases, Medical Microbiology and Hygiene, Heidelberg, Germany.
authors.forename: Nico T
authors.initials: NT
authors.lastname: Mutters
authors.affiliation: Division of Infectious Diseases, Department of Medicine, University Medical Center Freiburg, 79106 Freiburg, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Mischnik
authors.affiliation: National Reference Centre (NRC) for Staphylococci and Enterococci, Division of Nosocomial Pathogens and Antibiotic Resistances, Department of Infectious Diseases, Robert Koch Institute, Wernigerode Branch, Burgstraße 37, D-38855 Wernigerode, Germany. Electronic address: wernerg@rki.de.
authors.forename: Guido
authors.initials: G
authors.lastname: Werner
keywords: 23S rDNA; Linezolid; Resistance; VRE; Vancomycin-resistant enterococci