The Activity of Catalase
Many bacteria produce the enzyme catalase, which breaks down hydrogen peroxide, liberating oxygen. The simple test for
catalase can be very useful in distinguishing between organism groups. The hydrogen peroxide can be added directly to a slant
culture or to bacteria smeared on a clean glass slide. The test should not be performed with organisms growing on a bloodcontaining
medium because catalase is found in red blood cells.
||To observe bacterial catalase activity
||3% hydrogen peroxide
Pipette bulb or other aspiration device
Nutrient agar slant cultures of Staphylococcus epidermidis and Enterococcus faecalis
Clean glass slides
China-marking pencil or marking pen
- Divide a clean glass slide into two sections with your marking pen or pencil.
- With a sterilized and cooled inoculating loop, pick up a small amount of the Staphylococcus culture from the nutrient agar
slant. Smear the culture directly onto the left-hand side of the slide. The smear should be about the size of a pea.
- Sterilize the loop again and smear a small amount of the Enterococcus culture on the right-hand side of the slide.
- With the capillary pipette, place one drop of hydrogen peroxide over each smear. Be careful not to run the drops together.
Observe the fluid over the smears for the appearance of gas bubbles (see fig. 18.1). Record the results in the chart. Discard
the slide in a jar of disinfectant.
- Hold the slant culture of the Staphylococcus in an inclined position and pipette 5 to 10 drops of hydrogen peroxide onto the
surface with the bacterial growth. Observe closely for the appearance of gas bubbles.
- Repeat the procedure with the Enterococcus culture. Note whether oxygen is liberated and bubbling occurs.
|Figure 18.1 Slide catalase test. Staphylococcus epidermidis on the left produces a strong positive catalase reaction. Enterococcus faecalis on the right (cloudy area in drop of hydrogen peroxide) is negative in the catalase test.
Record your observations and conclusions in this chart.