coagulasepositive

Coagulase-positive refers to organisms that produce the enzyme coagulase, which converts soluble fibrinogen in plasma into insoluble fibrin, causing clot formation. In medical microbiology, this property is most commonly used to distinguish Staphylococcus aureus, which is coagulase-positive, from most other staphylococci that are coagulase-negative. The term can also apply to strains of other genera that produce coagulase, though its diagnostic relevance is strongest for staphylococci.

Coagulase exists in two forms. Bound coagulase, also known as clumping factor, is attached to the bacterial surface and can cause clumping of cells in plasma during slide tests. Free coagulase is secreted into the surrounding environment and induces clotting in plasma in tube tests. Together, these activities help some bacteria evade immune defenses by localizing fibrin around themselves and potentially facilitating infection.

Clinical and diagnostic significance is that the presence of coagulase activity is a key criterion in identifying Staphylococcus aureus in clinical specimens. Coagulase-positive S. aureus is associated with a range of infections, including skin and soft tissue infections, pneumonia, bacteremia, endocarditis, and toxin-mediated diseases. Coagulase testing is routinely used alongside other biochemical and molecular methods to confirm species identity.

Limitations and nuance include the fact that coagulase results are not infallible; some isolates may yield variable results, and a few other staphylococcal species can express coagulase under certain conditions. Therefore, coagulase status is generally interpreted in the context of additional phenotypic tests and, when needed, molecular or proteomic confirmation.