Vitek 2 identification card

Automated strain identification with Gram-positive (GP) Vitek 2 identification card (bioMerieux, France) according to the manufacturer’s instructions was performed. Susceptibility to methicillin was determined with cefoxitin discs (FOX 30 μg, Oxoid), according to the current EUCAST recommendations; mecA gene was detected with the PCR technique [15 (link)].
The first-line screening test to determine sensitivity to vancomycin and teicoplanin with AST-P580 cassettes in Vitek 2 system (bioMerieux, France) was performed, MIC values for VAN and TEI were determined with standard E-tests (bioMerieux, France). All strains which occurred less susceptible (even in the range of sensitivity, MIC VAN/TEI values at least 1 mg/L or higher), were classified to the further investigations. In the next step E-test GRD (glycopeptide resistance detection), (bioMerieux, France) was performed according to manufacturer’s guidelines, as well as agar dilution method, according to EUCAST ISO 20776–1. Forty seven MRSA strains that were both: positive in the GRD gradient test (MIC value equal to 8 mg/L or higher for VAN or TEI), and with MIC value for VAN ≥3 mg/L (in diagnostic manner at least 4 mg/L) in agar dilution method, were classified as an appropriate materials for analysis in this study.

Specimens were incubated at 37 °C for 24 h on Blood Agar and Mac-Conkey Agar. Staphylococcal isolates were identified using biochemical and morphological approaches. Multiple biochemical tests for the confirmation of S. aureus were performed on the Gram-positive cocci in clusters detected under a microscope. We identified S. aureus based on the presence of catalase and oxidase as well as coagulase activity and DNase activity in the S. aureus colonies on mannitol salt agar. The results of these biochemical tests were used to identify the organism. Presumptive VRSA confirmed by a Vitek 2 identification card (bioMerieux, Marcy l’Etoile, France) was used for automated strain identification according to the manufacturer’s instructions [37 (link),38 (link)].