A positive DNase would be seen with which organism?

A positive DNase would be seen with which organism?

• A. Escherichia coli
• B. Klebsiella oxytoca
• C. Proteus mirabilis
• D. Serratia marcescens

Answer: (D)

DNase testing checks whether a microbe makes an enzyme that breaks down DNA outside the cell. If an organism produces DNase, it hydrolyzes the DNA in the medium, producing a visible halo around the colony when the usual stain or indicator is applied. Serratia marcescens is known to be a DNase producer, so it yields a positive DNase result. Escherichia coli and Klebsiella oxytoca typically do not produce extracellular DNase and are negative, and Proteus mirabilis is usually negative as well, making Serratia marcescens the best match for a positive result.

DNase testing checks whether a microbe makes an enzyme that breaks down DNA outside the cell. If an organism produces DNase, it hydrolyzes the DNA in the medium, producing a visible halo around the colony when the usual stain or indicator is applied. Serratia marcescens is known to be a DNase producer, so it yields a positive DNase result. Escherichia coli and Klebsiella oxytoca typically do not produce extracellular DNase and are negative, and Proteus mirabilis is usually negative as well, making Serratia marcescens the best match for a positive result.