Coagulase reaction
In microbiology , the coagulase reaction is used to differentiate between pathogenic and (mostly) non- pathogenic staphylococci . The pathogenic staphylococci (e.g. Staphylococcus aureus ) are coagulase-positive (produce coagulase), the (mostly) non-pathogenic staphylococci (e.g. Staphylococcus epidermidis ) are coagulase-negative. To find out which strain is present, the bacteria are mixed with fibrinogen-containing plasma . If coagulase is given off by the bacterium, this leads to the clotting of fibrinogen , i. That is, clumps ( fibrin ) form.
The word coagulase implies an enzymatic activity. However, the term arose at a time when it was not yet possible to differentiate with regard to enzymatic activity. The coagulase is not an enzyme in the strict sense, but only an activator of prothrombin (analogous to factors V and X as well as calcium ions in blood clotting). Via a change in conformation, it leads to an activation of thrombin , which then causes fibrinogen to precipitate to fibrin .
The pathogenicity factor of the coagulase results from the fact that the bacterium wets itself with a protective layer of endogenous proteins when it enters the body through the coagulase (and also the clumping factor A ). These proteins hide the bacterium from the body's own immune system, making it difficult to eliminate.
The detection of the plasma coagulase is time-consuming (approx. 24 h), so that the simpler detection of the clumping factor is used. In contrast to the secreted plasma coagulase, the clumping factor A is a protein which is located on the cell wall and which binds directly to fibrinogen. The physiological function is analogous to that of plasma coagulase.
literature
- K. Becker, C. Heilmann, G. Peters: Coagulase-Negative Staphylococci . In: Clinical Microbiology Reviews . tape 27 , no. 4 , 2014, p. 870-926 , doi : 10.1128 / CMR.00109-13 , PMID 25278577 .
