About this test
What is the purpose of the test?
The purpose is to see if the microbe can use the compound urea as a source of carbon and energy for growth. Use of urea is accomplished by the enzyme urease .
How is presence of urease determined?
If urea can be used by the microbe, alkaline/basic breakdown products appear and the pH of the medium rises. A pH indicator in the medium changes color to indicate alkali/base production.
What medium is used?
The medium used is Christiansen’s urea broth. The medium is a nutrient broth to which 2.0% urea is added. The pH indicator is phenol red, which is red at neutral pH but turns yellow at pH < 6.8. It also changes to magenta or hot pink at pH >8.4.
How is the test performed?
An inoculum from a pure culture is transferred aseptically to a sterile tube of Christiansen’s urea broth. The inoculated tube is incubated at 35-37 C for 24 hours and the results are determined. A positive test consists of a color change from red to hot pink or magenta, indicating a pH change to alkaline/basic.
What reagents are added?
Performing this test in the VUMIE Online lab
Inoculation of Medium
1. Select the Christiansen’s urea broth medium.
2. Complete the process of a tube-to-tube aseptic transfer to inoculate the medium. Forgotten how to do these things? Watch the “Show Me How To” videos.
Incubation of the Inoculated Medium
3. Place the inoculated tube into the 35-37 C incubator.
Determination of Test Results
5. Incubate this test for only 24 hours.
6. Retrieve the incubated culture from the incubator.
7. Observe test result. The medium changes to magenta or hot pink in the presence of alkali/bases (indicating a positive test). In negative tests, there is rarely any growth and the color remains a pale orange.
8. Record test result.