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

controlIncubate broth tube at 370C. Examine at 24 hours. 

Result:

Positive Coagulase – a clot is formedNegative 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 microscopically. 

Positive - clumping Negative - no clumping