TRYPTONE WATER
Code: CM0087
A liquid medium for the production of indole by micro-organisms.
Typical Formula* | gm/litre |
Tryptone | 10.0 |
Sodium chloride | 5.0 |
pH 7.5 ± 0.2 @ 25°C | |
* Adjusted as required to meet performance standards
Directions
Dissolve 15g in 1 litre of distilled water and distribute into final containers. Sterilise by autoclaving at 121°C for 15 minutes.
Description
Tryptone Water is a good substrate for the production of indole because of its high content of tryptophan and it is more reliable than Peptone Water for this purpose. The ability of certain organisms to break down the amino-acid tryptophan with formation of indole is an important property which is used for the classification and identification of bacteria 1,2.
Technique
Kovac’s reagent: | |
paradimethylaminobenzaldehyde | 5 grams |
amyl alcohol | 75ml |
concentrated hydrochloric acid | 25ml |
1. Inoculate tubes of Tryptone Water, and incubate for 24-48 hours at 35°C.
2. Add 0.2ml of Kovac’s reagent and shake. Allow to stand for 10 minutes and observe the result.
A dark red colour in the amyl alcohol surface layer constitutes a positive indole test; no change in the original colour of the reagent constitutes a negative test.
Ehrlich reagent: | |
paradimethylaminobenzaldehyde | 4 grams |
absolute alcohol | 380ml |
concentrated hydrochloric acid | 80ml |
1. Inoculate tubes of Tryptone Water, and incubate for 24-48 hours at 35°C.
2. Withdraw a small portion of the culture and add an equal volume of the reagent. Shake the mixture and allow to stand for a few minutes; a rose colour indicates the presence of indole. If indole is present, this colour change may be accelerated by the addition of saturated potassium persulphate solution.
As an alternative, extract the indole by shaking the cultures with 1ml of ether, allow the mixture to stand for a few minutes and then add 0.5ml of Ehrlich reagent.
Incubation at 44°C for 24 hours has the specific advantage of detecting Escherichia coli, as this is the only organism present in water capable of producing indole at this temperature 3.
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.
Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Light straw coloured solution