Fig 1. MgrA is required for S. aureus clumping.

Washed S. aureus cells were incubated statically with either human plasma (A) or fibrinogen (B) and clumping was monitored by measuring clearing of the solution over time, as described in the methods section. Strains tested were the wild type USA300 LAC (black), an isogenic mgrA deletion (red), and the mgrA mutant complemented with a copy of mgrA expressed from an exogenous site on the chromosome (blue). Values represent averages and standard deviations of three separate experiments. Scanning electron micrographs of the same strains after incubation with fibrinogen for 2 h are shown in panels C-H. The white boxes in the top panels show the region magnified in the lower panels. Magnification is 5,000X in panels C, E, and G, and 45,000X in panels D, F, and H.