Identification of Bacteria: Catalase Test

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INTRODUCTION

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.

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

METHODS

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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