Definition – What is the coagulase test?
A coagulase test is performed to detect bacteria. Bacteria from the group of staphylococci can be distinguished by the so-called clumping factor. There are coagulase-positive staphylococci (Staphylococcus aureus) and coagulase-negative staphylococci (Staphylococcus epidermidis). The test is usually performed in a laboratory. The detection allows the therapy to be specifically adapted to the bacterium.
Indications for a coagulase test
A coagulase test is performed if staphylococci infection is suspected. This is a spherical bacterium. Some are also found on the skin of healthy people, but cause an infection in a wound.
This means that they are facultatively pathogenic. All staphylococci cause different diseases. A distinction is made between coagulase-positive staphylococci such as S. aureus, which as MRSA (methicillin-resistant Staphylococcus aureus) can lead to dangerous infections because it develops resistance to many antibiotics.
It is particularly feared in hospitals. An infection can lead to the development of abscesses and systemic infections. Examples of coagulase-negative staphylococci are S. epidermidis, which colonizes healthy skin, and S. haemolyticus.
These can cause local irritation and inflammation. In order to distinguish with which bacterium the wound is infected, the coagulase test is required. Indications may be: staphylococcal sepsis, dermatitis, abscesses, toxic shock syndrome, MRSA. The test is also increasingly used in the laboratory or in biology.
Preparation for a coagulase test
To perform a coagulase test, a sample of the infected area must first be taken. This can be done by a skin or nose swab, for example. There are special smear tubes for this purpose.
This is then sent to the laboratory, where the smear is distributed on a so-called agar plate. On this plate there are nutrients with which the bacteria are cultivated and form a colony. From the bacterial colonies, material can now be taken and used for the test.
Procedure
The material obtained from the cultivated bacterial colony is now transferred to a slide. There it is mixed with a fibrinogen-containing plasma. Fibrinogen is an enzyme of the coagulation cascade.
Coagulase-positive staphylococci have a so-called clumping factor A. This factor releases coagulase, which activates the enzyme thrombin via various mechanisms, which in turn cleaves fibrinogen into fibrin. The result is the formation of small clots.
Thus, the coagulase reaction is positive and it is a coagulase-positive staphylococcus, i.e. S. aureus. A somewhat outdated variant is the tube test. Here the bacterial colony is mixed with the plasma not on a slide but in a test tube. The result and the evaluation are the same. However, this test takes much longer than the slide test.
