title: A multi-center blinded study on the efficiency of phenotypic screening methods to detect glycopeptide intermediately susceptible Staphylococcus aureus (GISA) and heterogeneous GISA (h-GISA).
abstract: BACKGROUND
  To determine the true incidence of hGISA/GISA and its consequent clinical impact, methods must be defined that will reliably and reproducibly discriminate these resistant phenotypes from vancomycin susceptible S. aureus (VSSA).
  
  
  METHODS
  This study assessed and compared the ability of eight Dutch laboratories under blinded conditions to discriminate VSSA from hGISA/GISA phenotypes and the intra- and inter-laboratory reproducibility of agar screening plates and the Etest method. A total of 25 blinded and unique strains (10 VSSA, 9 hGISA and 6 GISA) were categorized by the PAP-AUC method and PFGE typed to eliminate clonal duplication. All strains were deliberately added in quadruplets to evaluate intra-laboratory variability and reproducibility of the methods. Strains were tested using three agar screening methods, Brain Heart Infusion agar (BHI) + 6 microg/ml vancomycin, Mueller Hinton agar (MH) + 5 microg/ml vancomycin and MH + 5 microg/ml teicoplanin) and the Etest macromethod using a 2 McFarland inoculum.
  
  
  CONCLUSIONS
  The ability to detect the hGISA/GISA phenotypes varied significantly between methods and phenotypes. BHI vancomycin and MH vancomycin agar screens lacked the ability to detect hGISA. The MH teicoplanin agar screen was more sensitive but still inferior to Etest that had a sensitivity of 98.5% and 99.5%, for hGISA and GISA, respectively. Intra- and inter-laboratory reproducibility varied between methods with poorest performance seen with BHI vancomycin.
  
  
  CONCLUSIONS
  This is the first multi-center blinded study to be undertaken evaluating various methods to detect GISA and hGISA. These data showed that the ability of clinical laboratories to detect GISA and hGISA varied considerably, and that screening plates with vancomycin have a poor performance in detecting hGISA.
authors: Radboud University Nijmegen Medical Centre, Nijmegen University Centre of Infectious Diseases, The Netherlands. a.voss@cwz.nl
authors: Andreas
authors: A
authors: Voss
authors: Johan W
authors: JW
authors: Mouton
authors: Erika P
authors: EP
authors: van Elzakker
authors: Ron G
authors: RG
authors: Hendrix
authors: Wil
authors: W
authors: Goessens
authors: Jan A
authors: JA
authors: Kluytmans
authors: Paul F
authors: PF
authors: Krabbe
authors: Han J
authors: HJ
authors: de Neeling
authors: Jacobus H
authors: JH
authors: Sloos
authors: Nefise
authors: N
authors: Oztoprak
authors: Robin A
authors: RA
authors: Howe
authors: Timothy R
authors: TR
authors: Walsh
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D006020:Glycopeptides / Q000494:pharmacology*; D015994:Incidence; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009426:Netherlands; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D017334:Teicoplanin / Q000494:pharmacology; D014640:Vancomycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D006020:Glycopeptides; D017334:Teicoplanin; D014640:Vancomycin