What Is A Coagulase Test?

You do coagulase tests to determine which bacteria produce the coagulase enzyme.

What Is A Coagulase Test?

In this article, we’ll tell you more about the procedures and principles of the coagulase test and more info about examples of Coagulase Positive Organisms and Coagulase Negative Organisms. First, let’s go through the coagulase test procedures.

Coagulase Test Procedures

There are two types of coagulase tests, and in this article, we’ll explain how to do these tests and what they identify.

Staphylococcus Aureus, for example, produces two different types of coagulase: bound and free. Before we explain the testing procedures, let’s discuss what bound and free coagulase are.

Bound coagulase doesn’t require a coagulase reacting factor. It binds to the cell wall of the bacteria.

This happens when the bound coagulase cells clump together, when the fibrinogen transforms the staphylococcal cell and when the bacterial suspension mixes with the plasma. 

Free coagulase, however, includes the plasma-coagulase reacting factor activating. A plasma coagulase-reacting factor is a by-product of a thrombin molecule, which then forms a complex.

When the complex responds to fibrinogen, it then produces a fibrin clot. 

You do these tests to determine bound or free coagulase. First, we’ll start with the slide test.

Step-By-Step Guide To The Slide Test

You use the slide test to search for bound coagulase. Here’s a step-by-step process on how to do the slide test.

  1. Put a drop of the physiological saline on each end of your slide, or you can place it on two individual slides.
  2. With a loop, a straight wire, or a wooden stick, you should combine a portion of the remote colony into each drop to make two thick suspensions.
  3. Include a globule of either human or rabbit plasma in one of your two suspensions. Mix them gently.
  4. Search for any clumping organisms within ten seconds of gently mixing.
  5. Don’t add plasma to your second suspension to identify the granular aspect of the organism from coagulase clumping.

Step-By-Step Guide To The Tube Test

You do the tube test to search for free coagulase. Here is a step-by-step process on how to do the tube test.

Step 1: Dilute plasma in physiological saline. Do this by mixing a combination of 0.2ml of plasma and 1.8ml of saline. 

Step 2: Take three smaller test tubes and designate them as such: T for Test, P for Positive Control, and N for Negative Control. You should place the Test tube in an eighteen to twenty-four hour period of broth culture. You should also put the Positive Control tube in an eighteen to twenty-four hour period of Staphylococcus Aureus broth culture and place Negative Control in sterile broth culture.

Step 3: You get a pipette and place 0.5ml of undiluted plasma in each of these tubes.

Step 4: Add five drops of 0.1ml of the Test organisms into the T tube. Place five drops of Staphylococcus Aureus culture in the P tube and five drops of sterile broth in the N tube.

Step 5: Once you’ve mixed these, incubate all of the tubes at 95-98.6 Degrees Fahrenheit. 

Step 6: After one hour, examine each tube for clotting. If none exists, look at the tubes for a maximum time of 6 hours at thirty-minute intervals.

How To Interpret The Coagulase Test

A negative result of the slide coagulase test will result in no clumps appearing, while a positive result will include clumps. 

You can identify a positive result in the tube test if a fibrin clot forms in the tube. A negative result of the tube test will have no fibrin clots. 

If there are clusters in both of your slides, it indicates that the organism you’re analyzing auto-agglutinates and is, therefore, incompatible with the slide test. You should make sure that you establish both negative slide test results using the tube test instead.

During the slide test, you may find false-positive results in the event of citrate utilizing bacteria. When this happens, you should also do a tube test to confirm the coagulase test results.

Examples Of Coagulase Positive Organisms

Here is a list of some examples of Coagulase Positive Organisms and a brief explanation of what each of these is.

Staphylococcus Aureus

S. Aureus is a round-shaped bacteria. It’s a member of the body’s microbiota, frequently found in your upper respiratory tract and the skin.

Staphylococcus Pseudintermedius

S. Pseudintermedius is a coccus bacteria that appear as grape-like clusters. It’s a pathogen that affects most domestic animals and can occasionally affect humans too. 

Staphylococcus Intermedius

S. Intermedius is a bacteria that consists of clustered cocci. Like S. Pseudintermedius, it can cause human infections and is pathogenic in animals. 

Staphylococcus Schleiferi

Schleiferi is a cocci-shaped bacteria with two subspecies, one of which is coagulase positive and the other negative. The positive subspecies is Staphylococcus schleiferi subsp. Coagulans. Generally, it’s a veterinary pathogen that affects household pets.

Staphylococcus Delphini

S. Delphini is a bacteria consisting of clustered cocci and single and paired cocci. Originally, S. Delphini was isolated from aquarium-raised dolphins who suffered from skin lesions.

Staphylococcus Hyicus

S. Hyicus is a bacteria that consists of clustered cocci. It’s a known animal pathogen that causes poultry, cattle, horses, and pigs diseases.

Staphylococcus Lutrae

S. Lutrae is a bacteria that was initially isolated from otters. 

All of these Coagulase Positive Organisms are bacteria with animal hosts.

Examples Of Coagulase Negative Organisms

Examples Of Coagulase Negative Organisms

Here is a list of examples of Coagulase Negative Organisms and brief explanations of what each of these is.

Staphylococcus Epidermidis

S. Epidermidis is a bacteria that are part of normal human flora, typically skin and occasionally mucosal.

Staphylococcus Saprophyticus

S. Saprophyticus is a bacteria that commonly cause UTIs in young, sexually active females.

Staphylococcus Warneri

S. Warneri is a bacteria that consists of spherical cells which appear in clusters. They’re commonly found as part of a human’s skin flora and on animals.

Staphylococcus Hominis

S. Hominis is a bacteria that consists of spherical cells in clusters. They occur on human and animal skin and contribute to body odor.

Staphylococcus Caprae

S. Caprae is a coccus bacteria initially isolated from goats but has also been isolated from humans.

These are examples of Coagulase Negative Organisms, but many more negative organisms exist outside this list.


Coagulase tests are done to identify organisms that produce this enzyme. Animals carry many Coagulase Positive Organisms. Look at whether your result is of bound or free coagulase.

When you find a negative result on your slide test, always check the results in a tube test to confirm the final result.

Jennifer Dawkins

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