The interaction of Streptococcus dysgalactiae with plasmin and plasminogen

The activation of plasminogen and the binding of plasmin by bacteria may have many effects which promote infection. The occurrence of such activities in streptococci is well documented; however, these are yet to be demonstrated for S. dysgalactiae. Consequently, the ability of this bacterium to activate mammalian plasminogen and bind either plasmin or its zymogen was investigated. Activation of bovine plasminogen was dependant on both the strain and the growth medium used for cultivation. Eighteen strains were able to activate bovine and ovine plasminogen and some of these also activated plasminogen from the horse, rabbit and pig. None activated human plasminogen and one strain (CE127) did not activate plasminogen from any source. Tricine-SDS PAGE and zymographic analysis of culture supernatants showed that bovine plasminogen was activated by four out of six strains at two locations corresponding to 16 kDa and 10 kDa. Following the growth of five strains in the presence of bovine plasminogen, all but strain CE127 bound high levels of plasmin activity. In contrast, following growth in human plasminogen none of the strains exhibited bound plasmin activity although all could bind human plasmin directly. All strains were also able to bind bovine and human plasminogen in such a way as to allow its activation by urokinase. We conclude that S. dysgalactiae is capable of activating mammalian plasminogen in a species-specific fashion and that the bacterium is also capable of binding plasmin and plasminogen with an apparent preference for bovine plasmin over human plasmin and/or plasminogen from either species.