coagulase

Coagulase is an extracellular enzyme produced by certain bacteria, most notably Staphylococcus aureus, that catalyzes the conversion of soluble fibrinogen in plasma into insoluble fibrin, resulting in clot formation. There are two major forms: free coagulase, secreted into the environment, and bound coagulase, also known as clumping factor, that remains attached to the bacterial cell surface.

Mechanistically, free coagulase forms a complex with prothrombin to create staphylothrombin, which then activates fibrinogen to fibrin, producing a clot. Bound coagulase interacts with fibrinogen directly at the bacterial surface and can cause clumping of bacteria in plasma samples. These activities can help bacteria resist immune clearance and may contribute to abscess formation and tissue invasion.

In laboratory practice, the coagulase test is used to distinguish Staphylococcus aureus, which is coagulase-positive, from most coagulase-negative staphylococci. The tube coagulase test detects free coagulase by observing clot formation in plasma after incubation, whereas the slide coagulase test detects bound coagulase via rapid agglutination of bacteria in the presence of plasma. Results can be influenced by factors such as culture age and test conditions; proper technique is important for accurate interpretation.

Clinical significance centers on the role of coagulase as a major virulence factor for S. aureus. Through fibrin formation, coagulase can shield bacteria from phagocytosis and facilitate local tissue invasion and dissemination. While coagulase-positive S. aureus is a common pathogenic threat, most coagulase-negative staphylococci do not produce coagulase and are associated with different clinical profiles, including device-related infections in some cases.