Sunday, December 26, 2010


Coagulase is an enzyme produced by some bacteria that reacts with prothrombin in the blood, forming a complex named staphylothrombin, which causes blood to clot by converting fibrinogen to fibrin. This mechanism protect bacteria from phagocytosis. Frequently coagulase test is used to distinguish between different types of Staphylococcus isolates.

Harvest blood from  a rabbit using EDTA to prevent coagulation. Separate plasma from blood cells deposit. Inoculate rabbit plasma with bacteria culture and incubate the tube in a 37 °C incubataor for 3 hours. Examine hourly the clot formation. If negative then continue incubation up to 24 hours.

Result is positive if the serum coagulates resulting a clot (or a solid block when the reaction is very intense). Handle the tube with care. The clot may be fragile and may be disrupted before reading the reaction.

Result is negative if  the plasma remains liquid.

Utilization of 2% Na citrate for blood harvesting is no longer recommended. Some bacteria can utilize citrate from plasma and false positive reactions may appear.

1. H. Raducanescu, V.Bica-Popii,1986. Bacteriologie veterinara, Ed. Ceres, Bucuresti.
2. Margaret Barnett, 1992. Microbiology Laboratory Exercises. Wm. C. Brown Publishers.

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