FIG. 4.

Kinetics of contact-mediated hemolysis by S. flexneri. A typical contact-mediated hemolysis reaction was performed, and the extent of hemoglobin release was monitored as a function of time (up to 60 min). The percentage of hemolysis was determined for wild-type S. flexneri M90T (filled triangles) or S. flexneri SF622 expressing ipaD (open circles), ipaD^Δ41-80 (closed squares), or ipaD^Δ81-120 (open squares). Negative controls included S. flexneri SF622 harboring pWPsf4 (no ipaD insert; filled circles) and S. flexneri BS547 (defective TTSS; open triangles). Complete hemolysis was determined by the addition of water. The values shown are the average of triplicates (± the standard deviation) and are from a representative experiment performed three times.