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Hippurate test

The figure shows the result of an hippurate test , where tube A is a negative control. Tube B contains Streptococcus agalactiae, which is hippurate positive and tube C contains Streptococcus dysgalactiae subsp. dysgalactiae, which is hippurate negative. Note that a colour change has occured in tube B because S. agalactiae is hippurate positive. Observe also that hippurate negative bacteria may give a faint colour change.

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

General

Some bacteria can hydrolyze hippurate to the amino acid glycine and benzoate by means of the enzyme hippuricase. Glycine can be detected with ninhydrin (2,2-Dihydroxyindane-1,3-dione), which reacts with free amino groups (-NH₂) and a blue product is formed.

Method

Suspend a loop-full of bacteria (for instance Campylobacter sp.) in 0.5 ml of sodium hippurate siolution.
Incubate the suspensionen at 37ºC during 2 h in a water bath.
Then carefully add 0.2 ml of ninhydrin solution without mixing.
Incubete the dube during another 10 min. at 37ºC before reading the result.

Positive test resultat: Deep blue colour.
Negative test result: Pale blue colour.

Use

The hippurate test is primarely used to distinguish between Campylobacter jejuni (hip+) and Campylobacter coli (hip-) and to distinguish between different streptococci (see figure).The test is also used, in combination with other methods, to type Brachyspira spp.

Updated: 2017-03-31.

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Hippurate test

General

Method

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