Either vancomycin or daptomycin was added to the cell cultures immediately before the addition of live staphylococci (10 5 -10 7 CFU/mL). Cells were then incubated for 18 hours. Daptomycin was obtained from Cubist Pharmaceuticals (Lexington, MA). Vancomycin was purchased via the Department of Pharmacy at Le Bonheur Children's Hospital (LBCH) from Hospira (Lake Forest, IL). Clinically achievable concentrations of each of the antibiotics, as previously tested in our laboratory [11] , were used (20 μg/mL).