Coagulase test is used to differentiate Staphylococcus aureus (positive) from Coagulase Negative Staphylococcus (CONS). Coagulase is an enzyme produced by S. aureus that converts (soluble) fibrinogen in plasma to (insoluble) fibrin. Staphylococcus aureus produces two forms of coagulase, bound and free.
- Slide coagulase test is done to detect bound coagulase or clumping factor.
- Tube coagulase test is done to detect free coagulase.
Slide Coagulase Test Procedure
- Take a clean grease free and dry glass slide
- Place a drop of plasma
- Place a drop of distilled water or saline next to the drop of plasma as a negative control
- Emulsify a portion of the isolated colony being tested in each drop, and make a smooth milky suspension (not clumpy).
- Rock the slide gently for 5 to 10 seconds and look for clumping (coagulation).
- Coagulase Positive: Macroscopic clumping in 10 seconds or less in coagulated plasma drop and no clumping in saline or water drop.
- Coagulase Negative: No clumping in either
drop
Note: All coagulase negative slides must be confirmed using tube coagulase test).
Tube Coagulase Test Procedure
- Emulsify several isolated colonies of test organism in 0.5 ml of rabbit plasma to give a milky suspension.
- Incubate tube at 35oC in ambient air for 4 hours.
- Check for clot formation, if negative at 4 hours, incubate at room temperature overnight and check again for clot formation.
Observation
- Coagulase Positive: Clot of any size eg. Staphylococcus aureus
- Coagulase Negative: No clot. eg. Staphylococcus epidermidis
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ReplyDeleteThe coagulase test serves as a vital tool in microbiology, aiding in the differentiation between Staphylococcus aureus and Coagulase Negative Staphylococcus (CONS). By detecting the presence of coagulase enzyme, specifically bound or free forms, this test provides valuable insights into bacterial identification. Whether employing the slide or tube method, careful execution of the procedure is essential for accurate interpretation of results, contributing to effective diagnosis and treatment of bacterial infections.
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