title: Etest versus vitek 2 vancomycin minimum inhibitory concentration testing methods for methicillin-resistant staphylococcus aureus: an antimicrobial stewardship initiative to evaluate the degree of discordance among methods at a rural tertiary hospital.
abstract: OBJECTIVE
  To evaluate the discordance between Vitek 2 and Etest vancomycin minimum inhibitory concentration (MIC) testing methods in methicillin-resistant Staphylococcus aureus (MRSA) isolates.
  
  
  METHODS
  Inclusion criteria consisted of MRSA isolates with blood, respiratory, or wound origin of culture, inpatient or emergency department location at time of culture and isolates with a Vitek 2 MIC reported. Isolates were subjected to Etest and the resulting MICs were compared to the corresponding Vitek 2 MICs, and both the rate and degree of discordance were evaluated.
  
  
  RESULTS
  Seventy-five MRSA isolates met the inclusion criteria. Etest resulted in an MIC value greater than that of Vitek 2 in 64 isolates (85.3%). Furthermore, of the 35 isolates with an MIC of ≤ 0.5 mcg/mL via Vitek 2, Etest reported 27 isolates with an MIC >1 mcg/mL. Of the 39 isolates with a Vitek 2 MIC of 1 mcg/mL, Etest reported 30 isolates with an MIC >1 mcg/mL.
  
  
  CONCLUSIONS
  We have demonstrated that Etest commonly reports MICs greater than 1 mcg/mL, even among isolates with MICs as low as ≤ 0.5 mcg/mL, according to Vitek 2. The clinical significance of these findings is unknown and would be an area of further study.
authors.affiliation: Avera McKennan Hospital & University Health Center, Sioux Falls, SD 57117, USA. brandon.bloomgren@avera.org
authors.forename: Brandon J
authors.initials: BJ
authors.lastname: Bloomgren
authors.forename: Brad R
authors.initials: BR
authors.lastname: Laible
mesh_terms: D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects*; D008826:Microbial Sensitivity Tests / Q000379:methods*; D062606:Tertiary Care Centers; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D014640:Vancomycin
keywords: Etest; Vitek 2; methicillin-resistant Staphylococcus aureus; vancomycin