Media and chemical substances.

For bacterial growth, tryptic soy broth (TSB) and Mueller-Hinton broth and agar (MHB and MHA) were obtained from Becton, Dickinson (Allschwil, Switzerland). Saline (0.9%) and sterile water (aqua ad iniectabilia) were obtained from Bichsel (Interlaken, Switzerland). AgNO₃ was acquired from Sigma and dissolved as stock solution in sterile water. For in vitro and in vivo experiments, the antibiotics daptomycin (DAP) (Cubicin; Novartis) and vancomycin (VAN) (Vancocin; Teva Pharma) were used. Stock solutions of DAP were prepared in 0.9% saline and always supplemented in vitro with 50 mg/liter (1.25 mmol/liter) calcium ions (CaCl₂) according to CLSI guidelines (27). Stock solutions of VAN were prepared in water.