title: Performance of different commercial methods for determining minimum inhibitory concentrations of glycopeptides and linezolid against blood isolates of Staphylococcus aureus.
abstract: The aim of this study was to determine the accuracy of commercial systems (VITEK®2, Etest and Sensititre®) in determining the minimum inhibitory concentrations of vancomycin, teicoplanin and linezolid of Staphylococcus aureus strains and to evaluate the reproducibility of each system in a clinical microbiology laboratory. In total, 115 strains of S. aureus isolated from blood cultures were tested with all three commercial methods as well as the broth microdilution method, which is designated as the standard for glycopeptides and linezolid. Fourteen different S. aureus strains were included in a reproducibility test for all methods and antibiotics. For these strains, antimicrobial susceptibility testing was repeated 10 times on different days with all four methods, each time using the same inoculum. All three commercial methods exhibited similar performance in categorisation of nearly all of the meticillin-susceptible S. aureus (MSSA) isolates. Discrepancies were registered for meticillin-resistant S. aureus (MRSA); 2.5% of the strains in the intermediate or resistant category with the VITEK 2 system were not recognised as resistant by Etest and Sensititre. Moreover, none of the three commercial methods provided accurate results compared with homemade broth microdilution. Reproducibility of vancomycin and teicoplanin was 100% with VITEK 2 and Sensititre and 98.75% with Etest. Microdilution showed a reproducibility of 95.6% with vancomycin and 83.1% with teicoplanin. In contrast to previous reports, the best agreement with microdilution was exhibited by VITEK 2 both for MSSA and MRSA. For the antibiotics tested, the best reproducibility was obtained with the VITEK 2 and Sensititre systems.
authors.affiliation: Department of Pathology and Diagnostics, Servizio di Microbiologia e Virologia, Azienda Ospedaliera Universitaria Integrata di Verona, Piazzale Stefani 1, 37100 Verona, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Lo Cascio
authors.affiliation: Department of Pathology and Diagnostics, Verona University, Strada Le Grazie 8, 37134 Verona, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Bazaj
authors.affiliation: Department of Pathology and Diagnostics, Servizio di Microbiologia e Virologia, Azienda Ospedaliera Universitaria Integrata di Verona, Piazzale Stefani 1, 37100 Verona, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Maccacaro
authors.affiliation: Department of Pathology and Diagnostics, Verona University, Strada Le Grazie 8, 37134 Verona, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Fontana
authors.affiliation: Department of Pathology and Diagnostics, Verona University, Strada Le Grazie 8, 37134 Verona, Italy.
authors.forename: A R
authors.initials: AR
authors.lastname: Centonze
authors.affiliation: Department of Pathology and Diagnostics, Servizio di Microbiologia e Virologia, Azienda Ospedaliera Universitaria Integrata di Verona, Piazzale Stefani 1, 37100 Verona, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Sorrentino
authors.affiliation: Department of Pathology and Diagnostics, Verona University, Strada Le Grazie 8, 37134 Verona, Italy. Electronic address: annarita.mazzariol@univr.it.
authors.forename: A
authors.initials: A
authors.lastname: Mazzariol
keywords: Etest; Sensititre; Teicoplanin; VITEK 2; Vancomycin