Principle

Citrate utilisation test is used to detect the ability of an organism to utilize sodium citratre as a sole source of carbon and ammonium salt as a sole source of nitrogen. Bacteria that grow in the medium turn the medium alkaline. This is indicated by the change of color of bromothymol blue indicator from green to blue.


Procedure:
  1. Inoculate Simmons citrate agar on the slant by touching a colony that is 18-24 hrs old with a straight wire.There is no need to stab the butt of the medium. Do not inoculate from the broth culture because the inoculum will be too heavy.
  2. Incubate at 35oC-37oC for up to 7 days.
  3. Observe the blue coloration of the media.
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Expected results:
Positive: Growth on the medium, with or without the change in color of the medium (blue).
Negative: Absence of growth

Quality control:
Positive: Klebsiella pneumoniae
Negative: Escherichia coli

 

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