What is this medium used for? Bacteria are identified based largely on what organic compounds they can break down. The range of compounds used depends on the collection of enzymes a species of bacteria can make. Gelatin is a protein that some bacteria can use because of an enzyme called gelatinase. Nutrient agar with 3% gelatin is used to determine whether the microbe can use the protein gelatin for carbon and energy.
How is gelatin use determined? Nutrient agar with 3% gelatin is a semisolid medium that will grow most microbes found in VUMIE Online. If gelatin can be digested, gelatinase will create pockets around colonies where no gelatin remains. All that is needed is a reagent to add to the agar after the colonies form that will show where gelatin is present, and where it is missing. This is accomplished by adding 5 ml of ammonium sulfate (saturated) to the streak plate. The chemical reacts with gelatin to create a cloud precipitate. Any place where that precipitated does not form is a location where there is no gelatin. Colonies that produce gelatinase will have clear zones surrounding them.
What is the content of this medium? The medium is a nutrient agar to which 3% gelatin is added. Several specialized media for this purpose are available. We decided to focus on use of nutrient agar with 3% gelatin. For details on the content of the base medium, see Nutrient Agar Plate.
How is the test performed? The process for conducting this test is explained in the Gelatinase Video found under the Tests tab above the VUMIE Online lab.