Coagulase is a bacterial enzyme that converts soluble plasma fibrinogen into insoluble fibrin, forming clots around cells.
Explanation
Several pathogenic bacteria produce coagulase as a virulence factor. The enzyme binds to prothrombin in the host to form staphylothrombin, which activates the host’s fibrinogen to fibrin. By generating a fibrin meshwork, the bacteria can shield themselves from phagocytes and other immune defenses. Coagulase exists in two forms: bound coagulase, also called clumping factor, which is attached to the bacterial surface, and free coagulase, which is secreted into the surrounding medium. Bound coagulase directly interacts with fibrinogen to cause agglutination, whereas free coagulase activates plasma coagulase-reacting factor to form a clot. Coagulase is produced by Staphylococcus aureus, Yersinia pestis and a few other species but not by most coagulase-negative staphylococci such as S. epidermidis. Its presence correlates with the ability to cause invasive infections like abscesses and septicemia.
Applications and examples
The coagulase test is widely used in clinical microbiology to identify S. aureus from other staphylococci. A slide test detects bound coagulase by mixing bacteria with plasma and looking for clumping. A tube test detects free coagulase by incubating bacteria with plasma and observing clot formation after several hours. A positive test suggests the organism is likely S. aureus or another coagulase-producing species and may require more aggressive treatment. Understanding coagulase helps explain how certain bacteria establish persistent infections by hiding within fibrin layers.
Coagulase highlights the ways microorganisms manipulate host physiology to survive and cause disease, and it remains an important diagnostic marker for differentiating staphylococcal species.
Related Terms: fibrinogen, Staphylococcus aureus, coagulase test, virulence factor, clot