performed if the result of the slide test is not clear, or when the slide test is negative and the Staphylococcus has been isolated from a serious infection.
Undiluted human plasma (preferably pooled) or rabbit plasma. The plasma should be allowed to warm to room temperature before being used. Plasma from EDTA (ethylenediamine – tetra – acetic acid) or citrate anticoagulated blood is usually used. Note: Occasionally citrate-utilizing organisms such as Klebsilla can cause the clotting of citrated plasma in the tube test. This can be prevented by adding heparin to the citrated plasma. It is also possible for human plasma to contain inhibitory substances which can interfere with coagulase testing. Adequate controls must be included for both slide and tube tests.
Method for slide test (to detect bound coagulase) Place a drop of physiological saline on each end of a slide, or on two separate slides. Emulsiy a colony of the test organism in each of the drops to make two thick suspensions. Note: Colonies from a mannitol salt agar culture are not suitable for coagulase testing. The organism must first be cultured on nutrient agar or blood agar. Add a drop of plasma to one of the suspensions, and mix gently. Look for clumping of the organisms within 10 seconds.