title: Evaluation of methods in detecting vancomycin MIC among MRSA isolates and the changes in accuracy related to different MIC values.
abstract: BACKGROUND
  Methicillin-Resistant Staphylococcus aureus (MRSA) presenting reduced susceptibility to vancomycin has been associated to therapeutic failure. Some methods used by clinical laboratories may not be sufficiently accurate to detect this phenotype, compromising results and the outcome of the patient.
  
  
  OBJECTIVE
  To evaluate the performance of methods in the detection of vancomycin MIC values among clinical isolates of MRSA.
  
  
  METHODS
  The Vancomycin Minimal Inhibitory Concentration was determined for 75 MRSA isolates from inpatients of Mãe de Deus Hospital, Porto Alegre, Brazil. The broth microdilution (BM) was used as the gold-standard technique, as well as the following methods: E-test® strips (BioMérieux), M.I.C.E® strips (Oxoid), PROBAC® commercial panel and the automated system MicroScan® (Siemens). Besides, the agar screening test was carried out with 3 µg/mL of vancomycin.
  
  
  RESULTS
  All isolates presented MIC ≤ 2 µg/mL for BM. E-test® had higher concordance (40%) in terms of global agreement with the gold standard, and there was not statistical difference among E-test® and broth microdilution results. PROBAC® panels presented MICs, in general, lower than the gold-standard panels (58.66% major errors), while M.I.C.E.® MICs were higher (67.99% minor errors).
  
  
  CONCLUSIONS
  For the population of MRSA in question, E-test® presented the best performance, although with a heterogeneous accuracy, depending on MIC values.
authors.affiliation: Department of Microbiology, Federal University of Health Science of Porto Alegre, Porto Alegre, RS, Brazil.
authors.forename: Fernanda Cristina Possamai
authors.initials: FC
authors.lastname: Rossatto
authors.affiliation: Department of Microbiology, Federal University of Health Science of Porto Alegre, Porto Alegre, RS, Brazil.
authors.forename: Letícia Auler
authors.initials: LA
authors.lastname: Proença
authors.affiliation: Department of Microbiology, Federal University of Health Science of Porto Alegre, Porto Alegre, RS, Brazil.
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Becker
authors.affiliation: Department of Microbiology, Federal University of Health Science of Porto Alegre, Porto Alegre, RS, Brazil.
authors.forename: Alessandro Conrado de Oliveira
authors.initials: AC
authors.lastname: Silveira
authors.affiliation: Department of Microbiology, Federal University of Health Science of Porto Alegre, Porto Alegre, RS, Brazil.
authors.forename: Juliana
authors.initials: J
authors.lastname: Caierão
authors.affiliation: Department of Microbiology, Federal University of Health Science of Porto Alegre, Porto Alegre, RS, Brazil.
authors.forename: Pedro Alves
authors.initials: PA
authors.lastname: D'Azevedo
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests / Q000379:methods; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin