Coagulase is a protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 produced by several microorganisms that enables the conversion of fibrinogen
Fibrinogen is a soluble plasma glycoprotein, synthesised by the liver, that is converted by thrombin into fibrin during blood coagulation. This is achieved through processes in the coagulation cascade that activate the zymogen prothrombin to the serine protease thrombin, which is responsible for...

 to fibrin
Fibrin is a fibrous, non-globular protein involved in the clotting of blood. It is a fibrillar protein that is polymerised to form a "mesh" that forms a hemostatic plug or clot over a wound site....

. In the laboratory
A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...

, it is used to distinguish between different types of Staphylococcus
Staphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....

isolates. Coagulase negativity excludes S. aureus. That is to say, S. aureus is coagulase-positive.

It is also produced by Yersinia pestis
Yersinia pestis
Yersinia pestis is a Gram-negative rod-shaped bacterium. It is a facultative anaerobe that can infect humans and other animals....


Coagulase reacts with prothrombin in the blood. The resulting complex is called staphylothrombin, which enables the enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....

 to convert fibrinogen to fibrin. This results in clotting of the blood. Coagulase is tightly bound to the surface of the bacteria S. aureus and can coat its surface with fibrin upon contact with blood. It has been proposed that fibrin-coated staphylococci resist phagocytosis making the bacteria more virulent. Bound coagulase is part of the larger family of MSCRAMM
MSCRAMM adhesin proteins mediate the initial attachment of bacteria to host tissue, providing a critical step to establish infection....

Coagulase test

The coagulase test is used to differentiate Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...

from coagulase-negative staphylococci
Staphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....

. S.aureus produces two forms of coagulase (i.e., bound coagulase and free coagulase). Bound coagulase otherwise known as "Clumping factor"
Clumping factor A
Clumping factor A, or ClfA, is a virulence factor from Staphylococcus aureus that binds to fibrinogen.ClfA also has been shown to bind to complement regulator I protein....

 can be detected by carrying out a slide coagulase test and free coagulase can be detected by doing a tube coagulase test.

Slide test

Slide coagulase test is run with a negative control to rule out auto agglutination. Two drops of saline are put on to the slide microscopic slide labeled with sample number, Test (T) and control (C). The two saline drops are emulsified with the test organism by using wire loop, straight wire, or wooden stick. Place a drop of plasma (rabbit plasma anti-coagulated with EDTA
Ethylenediaminetetraacetic acid, widely abbreviated as EDTA , is a polyamino carboxylic acid and a colourless, water-soluble solid. Its conjugate base is named ethylenediaminetetraacetate. It is widely used to dissolve limescale. Its usefulness arises because of its role as a hexadentate ligand...

 is recommended ) on the inoculated saline drop corresponding to test and mix well with wooden applicator stick. Rock the slide gently for about 10 seconds.
  • If positive: Macroscopic clumping would be observed in the plasma within 10 seconds and no clumping in the saline drop.
  • If negative: No clumping will be observed.

NOTE: If the slide coagulase test is negative, a tube test should follow as a confirmation. Clumping in both drops is an indication of auto-agglutination and therefore a tube test have to be carried out.

Tube test

The test uses rabbit plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

 that has been inoculated with a staphylococcal colony (i.e., gram positive cocci which is catalase
Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it catalyzes the decomposition of hydrogen peroxide to water and oxygen...

 positive). The tube is then incubated at 37 degrees Celsius for 1½ hours. If negative then continue incubation up to 18 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, the plasma remains liquid. The negative result may be S. epidermidis but only a more detailed identification test can confirm this, using biochemical tests as in Analytical Profile Index
    Analytical Profile Index
    The analytical profile index or API is a classification of bacteria based on experiments, allowing fast identification. It was invented in the 1970s in the United States by Pierre Janin of Analytab Products, Inc. Presently, the API test system is manufactured by bioMérieux...

     tests and BBL CRYSTAL methods.

  • List of coagulase-positive staphylococci: Staphylococcus aureus subsp. anaerobius, Staphylococcus aureus subsp. aureus, Staphylococcus delphini, Staphylococcus hyicus, Staphylococcus intermedius, Staphylococcus lutrae, Staphylococcus schleiferi subsp. coagulans.

  • List of coagulase-negative staphylococci of clinical significance: S.saprophyticus, S.cohnii subsp. cohnii, S.cohnii subsp. urealyticum, S.captitus subsp. captitus, S.warneri, S.hominis, S.epidermidis, S.caprae,S.lugdunensis.

External links

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