Identification of Bacteria: Catalase Test

Topics: Bacteria, Staphylococcus, Staphylococcus aureus Pages: 3 (570 words) Published: March 1, 2011

The enzyme catalase converts hydrogen peroxide (H2O2) to water and O2. The evolution of O2 causes bubbling. Thus, catalase-positive organisms that are mixed into hydrogen peroxide will cause bubbling (catalase-negative organisms will not). This test is good for distinguishing between Gram-positive cocci in chains (catalase negative) versus Gram-positive cocci in clusters (catalase positive).

The coagulase test is used to differentiate Staphylococcus aureus from coagulase-negative staphylococci. The test uses rabbit plasma that has been inoculated with a staphylococcal colony. The tube is then incubated at 37 degrees Celsius for 1½ hours. If negative then continue incubation up to 18 hours.

* If positive (i.e., the suspect colony is S. aureus), the serum will coagulate, resulting in a clot (sometimes the clot is so pronounced that the liquid will completely solidify). * If negative, the plasma remains liquid. The negative result may be S. epidermidis but only a more detailed identification test can confirm this, using biochemical tests as in API tests and BBL CRYSTAL methods.

Sterile swab, oxidase strap, microorganisms (Pseudomonas aeruginosa, E. coli)


A. Catalase

1. A drop of 3% H2O2 was placed on a glass slide.
2. A sterile loop was touched to the culture of the tested organisms. Visible mass of cell was picked. 3. The cell organism was mixed in a drop of hydrogen peroxide. 4. Immediate and vigorous bubbling was observed.

5. Obersevation was recorded in a table.

B. Coagulase

1. One drop of Test Latez was dispensed onto one of the circle on the reaction card and one drop of Control Latex on the other circle. 2. A sterile loop was touched to the culture of the tested organisms. Visible mass of cell was picked and mixed in the Test Latex. 3. Step 2 was repeated for the Control Latex.

4. The card was shaking for 20 seconds. Agglutination or clumping of the latex...
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