FIGURE 8.

BBA70-bound plasmin inhibits bacteriolytic effects of complement. 10 μg recombinant BBA70, ErpP, or ZQA70 was bound to magnetic beads and incubated with plasminogen (Plg). After washing, 2.5% NHS was added together with a final concentration of 0.16 μg/ml uPA, and the serum was preincubated with the beads at 37 °C. After 1 h, the treated serum samples were incubated with 1 × 10⁷ complement-sensitive E. coli DH5α cells. Following incubation at 37 °C for 2 h, serial dilutions were plated on agar plates, and cfu were determined the following day. DH5α cells incubated in GVB⁺⁺ (growth control) without serum were presumed to have a survival rate of 100%. As a negative control, E. coli DH5α cells were incubated in the presence of 2.5% NHS, resulting in complete killing of the cells. A, for serum preincubated with BBA70-bound plasmin, E. coli show nearly 100% survival, whereas no statistically significant survival is seen for controls omitting either uPA or plasminogen or when adding 50 mm tranexamic acid to plasminogen (+T). B, when serum was preincubated with ErpP-bound plasmin, E. coli show 100% survival. C, no statistically significant survival was observed for E. coli when we used ZQA70, which does not bind plasminogen. Error bars, S.E.