A basal medium to which carbohydrates and indicator may be added for fermentation studies.
|pH 7.2 ± 0.2|
Peptone Water may be used as a growth medium or as the basis of carbohydrate fermentation media, whilst a pure culture in Peptone Water is a convenient inoculum for a series of fermentation tubes or other diagnostic media.
Peptone Water, adjusted to pH 8.4, is suitable for the cultivation and enrichment of Vibrio cholerae from infected material1.
The medium was formerly used for the performance of the indole test, but now better results can be obtained by the use of Tryptone Water CM0087.
Peptone Water may be modified for use in carbohydrate fermentation tests by the addition of Andrade’s indicator. The indicator which is pink at pH 5.0 and yellow at pH 8.0 is prepared by adding sodium hydroxide to acid fuchsin until it becomes yellow. When added to Peptone Water it is colourless to slightly pink. Filter-sterilised `sugar’ solutions are added to the base medium after sterilisation. These solutions are usually at 10% w/v concentrations and it is important to allow for dilution of the Peptone Water when making up the initial volume of medium. A final concentration of 1% w/v sugar in Peptone Water is normally used but more expensive sugar can be used at 0.5%.
Andrade’s indicator may be made by adding 1N sodium hydroxide to a 0.5% solution of fuchsin until the colour just becomes yellow.
Appropriate safety precautions must be taken to avoid inhalation of, and skin contact with, acid fuchsin.
Both Peptone Water and Andrade Peptone Water are prepared and sterilised in the same manner except that an inverted fermentation tube (Durham tube) to detect gas production is included in Andrade Peptone Water containing glucose. Some organisms will utilise carbohydrate to produce acid only without gas formation. It is unnecessary to add Durham tubes to Peptone Water sugars other than glucose.
Precautions for Andrade Peptone Water sugars
Make sure that each individual bottle of Peptone Water sugar is correctly coded for the contained sugar.
Andrade Peptone Water is reddish-pink when hot; it should return to a colourless or a slightly pink colour when cooled to room temperature.
Some sugar solutions may affect the pH of the Peptone Water; check and correct if so.
Sub-cultures may be necessary to ensure purity of the inoculant. Mixed or contaminated cultures will give false reactions.
Andrade indicator will fade on prolonged storage; do not use beyond the expiry date.
Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at room temperature.