Coagulase-positive Staphylococci are human pathogens associated with serious infections. S. aureus can cause simple skin infections to life-threatening problems, such as endocarditis or heart infection. The bacteria is also associated with hospital infections, food poisoning and urinary tract infections, as well as mastitis, an inflammation that attacks cows. Other coagulase-positive Staphylococci include S. delphini, which causes infections in dolphins.
S. epidermidis is a common coagulase-negative staphylococcus found on the skin, which can also cause human infections. Other species of Staphylococci that do not produce coagulase include S. haemolyticus; S. warneri; S. schleiferi; S. caprae, first isolated in goats; S. saprophyticus, which is part of the vaginal flora but can cause genitourinary infections; and S. lugdunesis, a recently discovered species which can cause endocarditis.
Coagulase form blood clots by converting fibrinogen, a protein found in blood plasma, to fibrin, a fibrous protein which structure resembles a mesh. Although coagulase is often related to Staphyloccocci, this is not the only genus of bacteria that produce coagulase. Rod-shaped Yersinia pestis, a member of the family Enterobacteriaceae, causes serious infectious diseases, including the historical bubonic plagues.
The coagulase test is a very simple laboratory procedure. Technicians add the bacterial sample into a tube containing blood plasma and an anti-coagulant substance, such as citrate or heparin. After incubation, the presence or lack of clots determines if the Staphylococcus species in question is coagulase-negative or coagulase-positive. More often, the coagulase test is used to differentiate Staphylococcus aureus, a very resistant and common pathogen, from coagulase-negative species.