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Citrate test

The figure shows the result of a citrate test , by deep inoculation into "Simmons citrate tubes", where tube A contains a negativ control (no bacteria). Tube B contains Citrobacter freundii and tube C contains Escherichia coli. Note that a colour change has occured in tube B because C. freundii can grow on citrate as carbon source.

Image: Karl-Erik Johansson (BVF, SLU) and Lise-Lotte Fernström (BVF, SLU).

General

Some bacteria can utilize citrate as the only carbon source and the citrate test shows if the actual bacterium has this capability.

Method

Inoculate a tube containing citrate medium with a small amount of bacteria. It is also possible to streak or perform a deep inoculation into "Simmons citrate tube".
Incubate at 30-37ºC during 24-48 h.

Positive test result: growth in citrate medium or growth with colour change to blue in Simmon's citrate tube.
Negative test result: no growth in citrate medium eller growth but no colour change (still green colour) in Simmon's citrate tube.

Use

The citrate test is used to distinguish between, among others Citrobacter freundii and Escherichia coli.

Updated: 2018-06-06.

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Citrate test

General

Method

Use

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