Coagulase Test- Principle, Procedure, Types, Result, Uses


Staphylococci are Gram-positive bacteria that form clusters and are commonly found on the skin and mucous membranes of humans and animals. Some species of Staphylococci are harmless commensals, while others can cause infections ranging from minor skin infections to life-threatening diseases such as endocarditis, septicemia, and toxic shock syndrome. One of the most important and pathogenic species of Staphylococci is Staphylococcus aureus, which is responsible for many hospital-acquired and community-acquired infections.

To identify and diagnose S. aureus infections, it is essential to differentiate it from other Staphylococcal species that may have similar morphology and biochemical characteristics. One of the most reliable and widely used methods for this purpose is the coagulase test. The coagulase test is based on the ability of S. aureus to produce an enzyme called coagulase, which can cause the clotting or clumping of blood plasma. Coagulase production is considered a virulence factor of S. aureus, as it helps the bacteria evade the host immune system by forming a protective layer of fibrin around them.

The coagulase test can be performed in two ways: the slide test and the tube test. The slide test is a rapid and simple method that detects bound coagulase or clumping factor on the surface of the bacterial cells. The tube test is a more sensitive and specific method that detects free coagulase or extracellular coagulase in the culture supernatant. Both methods use plasma as a source of fibrinogen, which is converted to fibrin by coagulase. The presence or absence of clotting or clumping indicates whether the organism is coagulase positive or negative.

The coagulase test is useful for differentiating S. aureus from other Staphylococcal species, as S. aureus is usually coagulase positive, while most other Staphylococci are coagulase negative. However, there are some exceptions and limitations to this rule, which will be discussed later in this article. Therefore, the coagulase test should always be performed along with other tests to confirm the identity of S. aureus.

In this article, we will explain the principle, procedure, types, result, uses, and limitations of the coagulase test in detail. We will also provide some examples and images to help you understand this test better.