Coagulase

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Coagulase is an adhesin (EC [3.4.23.48]) produced by Staphylococcus aureus to localize an area of residence that converts fibrinogen to fibrin. In laboratory, it is used to distinguish between different types of Staphylococcus isolates. Coagulase negativity excludes S. aureus.

Coagulase is not an enzyme, despite its ending ("-ase"). It reacts with prothrombin in the blood. The resulting complex is called staphylothrombin, which causes blood to clot by converting fibrinogen to fibrin. Some coagulase is tightly bound to the surface of the bacteria S. aureus and coats its surface with fibrin upon contact with blood. Fibrin-coated staphylococci resist phagocytosis making the bacteria more virulent.

The coagulase test is used to differentiate Staphylococcus aureus from the other species of Staphylococcus. The test uses rabbit plasma that has been inoculated with a staphylococcal colony. The tube is then incubated at 37 degrees Celsius for 1-1/2 hours. If positive (i.e. the suspect colony is S. aureus), the serum will coagulate, resulting in a clot (sometimes the clot is so pronounced that the liquid will completely solidify). If negative (i.e. the suspect colony is S. epidermidis), the serum remains liquid.

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