Coagulase

In microbiology, the generally accepted criterion for identifying Staphylococcus aureus is its ability to produce free or bound coagulase (clumping factor) a surface-associated exotoxin. Specifically, S. aureus species secrete 2 types of coagulase, a staphylococcal coagulase and the "von Willebrand factor binding protein" both of which generate fibrin via prothrombin (Peetermans M et al. 2015). In fact, coagulase is not an enzyme in the true sense, but an exotoxin that acts as an activator of prothrombin. A conformational change on the surface leads to the activation of thrombin, which then causes the precipitation of fibrinogen into fibrin.

Coagulase activity is almost exclusively reserved for pathogenic staphylococci (e.g. Staphylococcus aureus). The (mostly) apathogenic staphylococci (e.g. Staphylococcus epidermis) are coagulase-negative. In order to examine the coagulase activity, the bacteria are mixed with fibrinogen-containing plasma. If the bacterium releases coagulase, this leads to coagulation of fibrinogen, i.e. lumps (fibrin) are formed.

The pathogenicity factor of coagulase results from the fact that the bacterium wets itself with a protective layer of the body's own proteins when it enters the body by means of the coagulase. Through this "protein envelope" the bacterium withdraws from the body's own immune defence. This makes its elimination more difficult.

The detection of plasma coagulase is time-consuming (approx. 24 h), so that the simpler method of detecting the clumping factor is used.

1. Peetermans M et al (2015) Coagulase Activity by Staphylococcus aureus: A Potential Target for Therapy? Semin Thromb Hemost 41:433-444.