Coagulase test

General

Some bacteria produce coagulase, which is an enzyme that converts fibrinogen to fibrin, which means that it can coagulate plasma. The ability to produce coagulase is assumed to be associated to the virulence of staphylococci. The test is used to distinguish between coagulase positive and coagulase negative staphylococci.

Method

1. Suspend one colony from the suspected pure culture in 0.5 ml of plasma from horse, rabbit or man.
2. Incubate at 37ºC.
3. Read the test after 4 h. If the result is negative (see below), continue with the incubation.
4. Perform the final read after 24 h.
   

• Positive reaction if the plasma coagulates and the coagulate is stable. It must not be dissolved upon stirring.
• Negative reaction if the plasma does not coagulate or if the coagulate is dissolved again upon stirring.

Coagulase test of Stahylococcus spp. The upper tube shows positive result (the plasma has coagulated) and the lower tube shows a negative result.

Use

The coagulase test is used to distinguish between Staphylococcus aureus from coagulase negative Staphylococcus spp. Note, however, that some strains of S. aureus can be coagulase negative, but it is unusual. Some strains of S. hyicus and S. intermedius can br coagulase positve. S. pseudintermedius is coagulase positive, but not until after 24 h.