Figure 4.

Display of protein A on the staphylococcal surface. Binding of CY3-labeled Ig to protein A was measured by capturing dark-field and fluorescent microscopy images with a charge-coupled device camera and superimposing the data. S. aureus OS2 (spa⁻) cannot express protein A; however, Ig binding was restored by transformation with plasmid encoding wild-type spa (pSpa). S. aureus SKM1 (srtA:ermC) failed to bind CY3-labeled Ig, a defect that was complemented by transformation with plasmids encoding wild-type srtA (pSrtA). S. aureus Newman (wild-type, wt) displayed protein A on the staphylococcal surface; however, the isogenic sortase knockout mutant SKM3 failed to bind CY3-labeled Ig.