title: Wild-type MIC distribution and epidemiological cut-off values in clinical Legionella pneumophila serogroup 1 isolates.
abstract: OBJECTIVE
  The purpose of this study was to establish wild-type (WT) distributions and determine the epidemiological cut-off values (ECOFF) in clinical L. pneumophila serogroup 1 isolates for 10 antimicrobials commonly used for the treatment of Legionella infections using a method feasible in a routine clinical laboratory.
  
  
  METHODS
  MICs of 183 clinical L. pneumophila serogroup 1 isolates, collected as part of an outbreak detection program, were tested using E-test methodology on buffered charcoal yeast extract agar supplemented with α-ketoglutarate (BCYE-α). The MICs were read after 2 days of incubation at 35 °C with increased humidity and without CO(2). ECOFFs were determined according to EUCAST methodology and expressed as WT ≤ X mg/L.
  
  
  RESULTS
  All antimicrobials showed a WT distribution, although the width varied from 2 two-fold dilutions to 8 dilutions, depending on antibiotic class. The ECOFFs determined were 1.0 mg/L for ciprofloxacin, 0.50 mg/L for levofloxacin, 1.0 mg/L for moxifloxacin, 1.0 mg/L for erythromycin, 1.0 mg/L for azithromycin, 0.50 mg/L for clarithromycin, 1.0 mg/L for cefotaxime, 0.032 mg/L for rifampicin, 16 mg/L for tigecycline, and 8 mg/L for doxycycline.
  
  
  CONCLUSIONS
  All isolates were inhibited by low concentrations of the fluoroquinolones and macrolides tested, with somewhat higher MICs for the fluoroquinolones. Rifampicin was found to be the most active against L. pneumophila isolates in vitro. These data can be used as a reference for the detection of resistance in clinical L. pneumophila isolates and as a setting of clinical breakpoints.
authors.affiliation: Regional Laboratory of Public Health, Haarlem 2035 RC, The Netherlands. j.bruin@streeklabhaarlem.nl
authors.forename: Jacob P
authors.initials: JP
authors.lastname: Bruin
authors.forename: Ed P F
authors.initials: EP
authors.lastname: Ijzerman
authors.forename: Jeroen W
authors.initials: JW
authors.lastname: den Boer
authors.forename: Johan W
authors.initials: JW
authors.lastname: Mouton
authors.forename: Bram M W
authors.initials: BM
authors.lastname: Diederen
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D006801:Humans; D016952:Legionella pneumophila / Q000187:drug effects* / Q000302:isolation & purification*; D007877:Legionnaires' Disease / Q000382:microbiology*; D008826:Microbial Sensitivity Tests / Q000379:methods*
chemical_list: D000900:Anti-Bacterial Agents