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The GAS M49 591 chromosomal background was generated previously by insertional inactivation of the ska gene (16). The construction of the epf, emm49, and prtF2 mutant strains from GAS M49 591 has been described previously (17?0). The GAS strains were cultured in Todd-Hewitt broth (THB; Invitrogen) at 37 under a 5 CO2 and 20 O2 atmosphere. Materials. Pooled normal plasma and plasma deficient in
N activator streptokinase might contribute to contact system activation by S. pyogenes. Here, we report that the human contact system is activated by the action of streptokinase. The role of secreted and surfacebound streptokinase in this process was investigated by comparing an M49 S. pyogenes wild-type strain with its isogenic ska mutant, which is unable to trigger plasmin activity in human plas