Some bacteria produce coagulase, an enzyme and as a precursor of thrombin like substance which coagulate plasma. There are two kinds of coagulase which could be present in the microorganism the free coagulase and the bound coagulase. This enzyme is demonstrated in vitro by two methods. The Test Tube Method The Slide Method Differentiate pathogenic from non-pathogenic Staphylococcus

Tube Method: The method measures free coagulase.

Materials: Citrated or heparinized human or rabbit plasma is diluted with isotonic saline or other suitable diluent Overnight broth culture of microorganism.

Procedures: Place about 0.5ml of diluted plasma in each of 2 test tubes. To one tube add 5 drops of an overnight broth culture of the organism. Do not place anything in the other tube which serves as control Incubate broth tube at 370C. Examine at 24 hours.

Result: Positive Coagulase a clot is formed Negative Coagulase no clot is formed

Slide Method: This usually detects bound coagulase, which is the clumping factor attached to the cells and acts directly on the fibrinogen. Procedures: Divide the slide into two sections with grease pencil. Place a small drop of normal saline on each area. Emulsify one or two colonies of microorganism on blood agar plate on each drop to make a smooth suspension. Add a drop of undiluted plasma to one of the drop of saline and stir gently with a wire loop. Do not put anything in the other drop that serves as control. Observe for clumping of the microorganism