Figure 4.

Early time-kill assay. The indicated four CA-MRSA MW2 strains and derivatives, all with equivalent MIC, were exposed to three concentrations (in μg/mL) of ceftaroline (CPT: 1/2 MIC, MIC, and 2 × MIC) in broth at 37 °C (Materials and Methods). Aliquots were removed every hour and viable cell titers were determined by serial dilution and plating on MHA plates without drug. The data represent the results of three biologically independent determinations and curves are plotted ± SD. Note that for CPT 0.5 and 1.0 conditions, the double arlRS/vraSR mutant consistently reduces viable cell titer faster than the single vraSR mutant strain.