What is indicated by a positive DNase result after adding 0.1 HCl to the plate?

A positive DNase result after adding 0.1 HCl to the plate is indicated by clearing around the colony. This occurs because DNase is an enzyme produced by certain bacteria that catalyzes the hydrolysis of DNA. When the DNase is secreted by the bacteria, it breaks down the DNA present in the agar surrounding the colony.

Upon adding HCl, the acid precipitates the DNA, which is normal; however, where the DNase has acted and broken down the DNA, that area will remain clear as the DNA is no longer present to precipitate. This distinct clearing is a strong indicator of a positive DNase test and signifies that the organism is capable of producing DNase.

In contrast, intense coloration, cloudiness, or surface growth may not provide the specific information needed to confirm DNase activity and therefore do not represent a positive result in this case.