No plasma is added to the second suspension. This is used to differentiate any granular appearance of the organism form true coagulase clumping.
Clamping within 10 secs ------------------------ S.aureus No clumping within 10 secs-----------No bound coagulase produced.
Positive coagulase control: Staphylococcus aureus. Negative coagulase control: Escherichia coli or Staphylococcus epldermids
Method for tube test (detect free coagulase)
Dilute the plasma 1 in 10 in physiological saline (mix 0.2 ml of plasma with 1.8ml of saline). Take three small test tubes and label:
= Test organism (18-24h broth culture)
Positive control (18-24h staph. Aureus broth
culture) Neg = Negative control (sterile broth) A suitable broth is brain heart infusion Pipette 0.5ml of the diluted plasma into each tube. Add 5 drops (about 0.1ml) of the test organism culture to the
tube labeled ‘T’.