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SOP

Coagulase Test for Staphylococcal Identification

SOP for detecting coagulase enzyme to differentiate Staphylococcus aureus from other staphylococci.

Last verified 1 month ago 1 min read Microbiology Bacteriology Biochemical Testing Identification #microbiology #Biochemical Test #coagulase test #staphylococcus aureus
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Document Control
Version
1.0
Effective
Aug 28, 2026
Reviewed
Aug 29, 2026
Department
Microbiology
Principle

Coagulase converts fibrinogen to fibrin, causing plasma to clot. Slide test detects bound coagulase (clumping factor); tube test detects free coagulase.

Standard Operating Procedure: Coagulase Test

1. Purpose: Differentiate S. aureus (coagulase-positive) from Coagulase-Negative Staphylococci (CoNS).

2. Specimen: Pure 18-24h bacterial culture on non-blood agar.

3. Reagents: Rabbit plasma (with EDTA), sterile saline, glass slides, test tubes.

4. Procedure:

  • Slide Test (Bound coagulase): Emulsify colony in drop of saline. Add drop of rabbit plasma. Mix. Observe for macroscopic clumping within 10 seconds.
  • Tube Test (Free coagulase): Emulsify colony in 0.5 mL rabbit plasma. Incubate at 37°C. Check for clot formation at 1h, 2h, and 4h. If negative, leave at room temperature overnight (max 24h).

5. Interpretation: Clumping/clotting = Positive. No clumping/clotting = Negative.

6. QC: S. aureus ATCC 25923 (Positive), S. epidermidis ATCC 12228 (Negative).

Frequently Asked Questions

Rabbit plasma lacks inhibitors to staphylocoagulase and does not contain fibrinolytic enzymes that might dissolve the clot.