Citrate Test
Principle
-
The citrate test is used to determine the ability of a bacterium to utilize citrate as sole source of carbon and production of alkaline by products.
-
Bacteria that utilize citrate can also extract nitrogen from the ammonium salt,with production of ammonia (NH4),leading to alkalinisation of medium by producing ammonium hydroxide.
-
A pH indicator in the medium Bromthymol blue which is yellow below pH 6.0 and blue above pH 7.6 , detects the presence of this compound by turning blue.
Methodology
-
Inoculate the Simmon’s citrate lightly on the slant by touching the tip of a needle to a colony that is 24 hours old. Note: No need to stab into the butt of the tube. Do not inoculate a broth culture,because the inoculum will be too heavy.
-
Incubate at 35 to 37 c for 48 to 72 hours.
-
Observe for development of blue colour,indicating alkalinization.
Result
![Citrate_test Citrate_test](http://14.139.56.154:82/file.php/183/Topic-15/Citrate_test.jpg)
Citrate Test
Quality control
- Positive : Klebsiella pneumoniae
- Negative : Escherichia coli
|
Last modified: Monday, 4 June 2012, 7:58 AM