About this test
What is the purpose of the test?
The purpose is to see if the microbe can use DNA as a source of carbon and energy for growth. Use of DNA is accomplished by an enzyme called DNase .
How is DNase activity determined?
A medium containing DNA and an indicator is used. The indicator complexes with intact DNA , making the medium appear mint green. When DNA is digested, the indicator changes from mint green to clear. Halos surrounding colonies is indicative of their ability to digest the DNA in the medium due to the presence of DNase .
What medium is used?
The medium used is DNase agar with methyl green. The medium is a nutrient agar to which DNA is added. The indicator methyl green produces a mint green medium.
How is the test performed?
An inoculum from a pure culture is streaked on a sterile plate of DNase agar. The inoculated plate is incubated at 37 C for 24 hours. Presence of clear halos surrounding colonies is positive for their ability to digest the DNA and thus indicates presence of DNase.
What reagents are added?
None.
Performing this test in the VUMIE Online lab
Inoculation of Medium
1. Select the DNase agar with methyl green plate medium.
2. Complete the process of a tube-to-plate aseptic transfer to inoculate the medium.
Incubation of the Inoculated Medium
3. Place the inoculated tube into the 35-37 C incubator.
4. Press the New Day button to move forward 24 hours.
Determination of Test Results
5. Incubate this test for only 24 hours.
6. Retrieve the incubated culture from the incubator.
7. Observe the color of the medium surrounding colonies in the plate. The culture showing clear halos around colonies is capable of breaking down DNA. The medium surrounding colonies without DNase remains unchanged.
Uninoculated DNase Agar with Methyl Green
Positive Test – halos clearing agar