Mouse skin passage of Streptococcus pyogenes results in increased streptokinase expression and activity

The plasminogen activator streptokinase has been proposed to be a key component of a complex mechanism that promotes skin invasion by Streptococcus pyogenes. This study was designed to compare ska gene message and protein levels in wild-type M1 serotype isolate 1881 and a more invasive variant recovered from the spleen of a lethally infected mouse. M1 isolates selected for invasiveness demonstrated enhanced levels of active plasminogen activator activity in culture. This effect was due to a combination of increased expression of the ska gene and decreased expression of the speB gene. The speB gene product, SpeB, was found to efficiently degrade streptokinase in vitro.