Citrate Test
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Principle
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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.
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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.
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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
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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.
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Incubate at 35 to 37 c for 48 to 72 hours.
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Observe for development of blue colour,indicating alkalinization.
Result
Citrate Test
Quality control
- Positive : Klebsiella pneumoniae
- Negative : Escherichia coli
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Last modified: Monday, 4 June 2012, 7:58 AM
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