Catalase is an enzyme that decomposes hydrogen peroxide into oxygen and water. Excluding the Streptococci, most aerobic and facultative anaerobic bacteria possess catalytic activity.
Methodology
Hydrogen peroxide forms as one of the oxidative end products of aerobic
carbohydrate metabolism. Catalase converts hydrogen peroxide into water
and oxygen. The catalase test is commonly used to differentiate
streptococci (negative) for staphylococci (positive).
Specimen Requirements
Well -isolated colonies of an 18-24 hour culture.
Reagents and Equipment
3% Hydrogen peroxide, Clean glass slide, Dropper, Bacteriological Loop
Controls
Positive: Staphylococcus aureus
Negative: Streptococcus sp.
Procedure:
1. With loop or applicator stick, transfer cells from the center of a
well-isolated colony to a glass slide.
2. Add 1-2 drops of the 3% Hydrogen peroxide to the bacterial cells
note: It is recommended to use this order instead of adding the
organism to the reagent,
particularly if iron containing loops are used, due
to false positives
Interpretation
Positive: rapid , appearance of sustained gas bubbles
Negative: No gas bubble production
Coagulase catalyzes the conversion of fibrinogen to fibrin in blood plasma. The network of fibrin formed in host tissue infected with coagulase producing organisms serves to protect the bacterium from the defenses of the host. This characteristic is a primary indicator of virulence among staphylococci. This test can be used to differentiate Staphylococcus aureus from Staphylococcus epidermidis as well as streptococcus organisms. Coagulation within 24 hours is indicative of Staphylococcus aureus.
Materials
Well-isolated colonies, Citrated rabbit plasma (1:4 dilution), Pipettes, Small
test tubes
Procedure
1. Heavily inoculate a tube containing 0.5 ml rabbit plasma with your
unknown organism.
2. Incubate the mixture at 37degrees C .
3. Examine the plasma tube for coagulation by gently tilting the tube.
4. Observe tube(s) at 0.5, 1, 2, and 4-hour intervals.
Note: If tube has not clotted after 4 hours, then
incubate for 24 hours and then read.
Interpretation
Positive: Staphylococcus aureus
Negative: Staphylococcus epidermidis, Streptococcus sp.