Staphylokinase Control ofStaphylococcus aureusBiofilm Formation and Detachment Through Host Plasminogen Activation

Abstract

Staphylococcus aureus biofilms, a leading cause of persistent infections, are highly resistant to immune defenses and antimicrobial therapies. In the present study, we investigated the contribution of fibrin and staphylokinase (Sak) to biofilm formation. In both clinical S. aureus isolates and laboratory strains, high Sak-producing strains formed less biofilm than strains that lacked Sak, suggesting that Sak prevents biofilm formation. In addition, Sak induced detachment of mature biofilms. This effect depended on plasminogen activation by Sak. Host-derived fibrin, the main substrate cleaved by Sak-activated plasminogen, was a major component of biofilm matrix, and dissolution of this fibrin scaffold greatly increased susceptibility of biofilms to antibiotics and neutrophil phagocytosis. Sak also attenuated biofilm-associated catheter infections in mouse models. In conclusion, our results reveal a novel role for Sak-induced plasminogen activation that prevents S. aureus biofilm formation and induces detachment of existing biofilms through proteolytic cleavage of biofilm matrix components.

Tissue Plasminogen Activator Coating on Implant Surfaces Reduces Staphylococcus aureus Biofilm Formation

“…Plasmin is a broad-spectrum protease, so it potentially also cleaves other proteins involved in biofilm formation, further strengthening the antibiofilm effect. As tPA has increased activity in the presence of fibrin (27), tPA coating might selectively induce increased fibrinolysis in response to abundant fibrin, which is one of the essential structural components of the S. aureus biofilm matrix (11). tPA coating displayed a robust ability to reduce biofilm formation by clinical isolates from biofilm-related infections, whereas it had no effect on staphylokinase-overexpressing strains, which are usually not associated with biofilm infections (11).…”

“…As tPA has increased activity in the presence of fibrin (27), tPA coating might selectively induce increased fibrinolysis in response to abundant fibrin, which is one of the essential structural components of the S. aureus biofilm matrix (11). tPA coating displayed a robust ability to reduce biofilm formation by clinical isolates from biofilm-related infections, whereas it had no effect on staphylokinase-overexpressing strains, which are usually not associated with biofilm infections (11). This is conceivably due to the fact that staphylokinase-overexpressing strains have already exerted their full effect of local plasminogen activation, which is similar to the mechanism of action of tPA coating.…”

“…Biofilms grown on 13-mm Thermanox polyester coverslips in 300 l of medium in the wells of a 24-well plate were visualized with a scanning electron microscope as described previously (11).…”

“…After an initial adhesion phase, bacteria divide, deposit an extracellular matrix, and develop complex threedimensional biofilm structures. Recently, several studies have demonstrated that, at this stage, fibrin deposits act as a central structural component of the S. aureus biofilm matrix (11)(12)(13)(14). Intriguingly, certain S. aureus strains secrete large amounts of staphylokinase, a bacterial plasminogen activator (15)(16)(17).…”

“…Intriguingly, certain S. aureus strains secrete large amounts of staphylokinase, a bacterial plasminogen activator (15)(16)(17). Release of staphylokinase induces local activation of fibrinolysis, resulting in less fibrin deposition on the implant surface and reduced bacterial attachment and biofilm formation (11). Therefore, we hypothesize that precoating of the surfaces of indwelling medical devices with plasminogen activators might reduce the risk of attachment of free-floating bacteria with subsequent biofilm formation.…”