FIG 7.

Homogeneous DAP^r MRSA strains do not display the seesaw effect without DAP induction. DAP^r strain CB5014 grown overnight in the absence (A) and in the presence (B) (strain CB5014IndD) of sublethal concentrations of DAP (0.5× MIC with 2 μg/ml 50 mg/liter Ca²), after which the adjusted inoculum was plated onto MH agar containing 0.5× MIC of DAP (2 μg/ml). OXA Etest strips were placed on the plates, and the plates were incubated for 24 h. (C) Western blot (WB) analysis of the PBP 2a present in cell membrane extracts collected from cells as described in the legend to panel A. (D) Quantitation of mecA mRNA by real-time RT-PCR using RNA prepared from CB5014 and CB5014IndD. Relative fold changes are shown; 16S rRNA was used as an internal control. # and *, the fold change was significantly greater than that for the control (P < 0.05 and P < 0.01, respectively). C, control; D, daptomycin; Ox, oxacillin; D/O, daptomycin-oxacillin.