Expert: Florence M Rollwagen - 7/17/2008

Question
Hi,

I have two questions:

1. What is the medical significance of DNase, coagulase and catalase?

2. A catalase test is performed on an isolated colony on a blood agar plate and bubbles appear.  The test is repeated by performing a spot catalase test on a colony from the same pure culture. This time there are no bubbles. How can you explain the difference in results?

Thanks VERY much.

Answer
Hi JJ:  

DNase may help bacteria escape from phagocytes such as neutrophils that have engulfed them.  DNase is an enzyme that breaks down DNA.  It is associated with pathogenicity of bacteria.  

Coagulase is an enzyme which pathogenic bacteria secrete.  It functions to form clots of fibrin around the bacteria, which inhibit phagocytes from engulfing them.

Catalase is an enzyme which bacteria use to ease the effects of oxygen free radical toxicity.  It converts peroxide or superoxide to oxygen and water.  The bubbles that you see are oxygen bubbles from the enzymatic reaction.

I can’t believe that these answers are not in your textbook.


As for your second question, I suspect that the culture may have been old, or that insufficient inoculum was placed on the spot.

FM Rollwagen, PhD