CITRATE UTILIZATION TES
This test is one of several techniques used to assist in the identification of enterobacteria. The test is based on the ability of an organism to use citrate as its only source of carbon and ammonia as its only source of nitrogen.
The test organism is cultured in a medium which contains sodium citrate, an ammonium salt, and the indicator bromo – thymol blue. Growth in the medium is shown by turbidity and a change in colour of the indicator from light green to blue, due to the alkaline reaction, following citrate utilization.
Required Koser’s citrate medium or Simmon’s citrate agar.
Using a sterile straight wire, inoculate 3-4ml of sterile Koser’s citrate medium with a broth culture of the test organism. Note: Care must be taken not to contaminate the medium with carbon particles, such as from a frequently flamed wire.
Incubate the inoculated broth at 35 – 37OC for up to 4 days, checking daily for growth.