Surface bound plasmin promotes migration of Streptococcus pneumoniae through reconstituted basement membranes.

Penetration of basement membrane is believed to be an essential step in the pathogenesis of bacterial meningitis. Consequently Streptococcus pneumoniae strains were tested for their ability to adhere to reconstituted basement membrane (Matrigel) and in a proceeding step penetrate this membrane by the use of surface activated plasmin. A majority of S. pneumoniae strains tested were found to adhere to reconstituted basement membrane as well as to the purified laminin component. Three out of seventeen strains also adhered to the collagen IV component. All the investigated strains also demonstrated a capacity to bind plasminogen with up to 42,000 plasminogen binding sites per bacterium as estimated by Scatchard analysis. Two strains selected for optimal adhesion and plasminogen binding were further tested for basement membrane penetration using a dual chamber model. Our data show that penetration was achieved within 3-4 h in the presence of plasminogen whereas without plasminogen no strain was able to penetrate during a 21 h incubation. The results suggest a potential role of surface associated plasminogen in bacterial penetration of basement membranes and extracellular matrix.