Characterization of S. aureus ST93 Isolates

The 56 S. aureus ST93 isolates analyzed in this study have been described previously (Coombs et al. 2012 (link)). However, alternative strain names were assigned to the isolates and these are listed in supplementary figure S1, Supplementary Material online. Isolates were grown in Heart Infusion Broth (Oxoid), incubated at 37 °C. Oxacillin susceptibility testing using Etest was performed according to manufacturer’s instructions (AB Biodisk). For δ-hemolysin (Hld) expression levels, bacteria were grown overnight at 37 °C in tryptone soy broth (TSB, Oxoid). Cultures were then diluted 1:100 into fresh media and incubation continued with shaking (180 rpm) for approximately 24 h (OD600 2.0). Culture supernatants were harvested by centrifugation and filter sterilized. These assays were performed with at least biological triplicates for each S. aureus isolate. Hld was measured using high-performance liquid chromatography on an Agilent Technology 1200 Series system with an analytical Agilent Eclipse XDB-C18 (4.6 mm × 150 mm) column, coupled with electrospray ionization mass spectrometry as described (Gao et al. 2013 (link)).