Identification and Antimicrobial Susceptibility of S. aureus

Clinical specimens and nasal swabs were cultivated according to standard procedures on Mueller–Hinton broth at 37 °C for 24 h, mannitol salt agar at 37 °C for 48 h, and on Columbia blood agar at 37 °C for 24 h, before molecular studies. S. aureus was presumably identified by catalase slide test, coagulase tube test, and Pastorex Staph-Plus test, performed according to the manufacturer’s protocol (Bio-rad, Marnes-la-Coquette, France) [2 ,52 (link)]. Antimicrobial susceptibility testing was achieved by the VITEK-2 Antimicrobial Susceptibility Testing automated systems, using the AST-P580 card according to the manufacturer’s specifications (bioMérieux, Marcy l’Etoile, France) and EUCAST clinical breakpoints (version 1.3) to define susceptibility. Species confirmation was achieved by Matrix-Assisted Laser Desorption Ionization Time-of-Flight mass spectrometry (MALDI Biotyper system, Bruker Daltonics, Bremen, Germany) and, additionally, by PCR targeting the S. aureus nuc gene as described elsewhere [53 (link),54 (link),55 (link)]. DNA was extracted from S. aureus cells using the QIA amp tissue kit (Qiagen, Hilden, Germany) by following the manufacturer’s recommendations. Methicillin resistance was confirmed by PCR targeting mecA and mecC, respectively [56 (link),57 (link)].