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.
- 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.
- Incubate at 35oC-37oC for up to 7 days.
- Observe the blue coloration of the media.
Positive: Growth on the medium, with or without the change in color of the medium (blue).
Negative: Absence of growth
Positive: Klebsiella pneumoniae
Negative: Escherichia coli
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