Tryptone Broth, HiVeg® (Tryptone Water, HiVeg®)

Principle And Interpretation

Tryptone Broth, HiVeg® is prepared by using HiVeg® Hydrolysate in place of tryptone which makes the medium free of BSE/TSE risks. HiVeg® hydrolysate is a good substrate for indole production because of its high tryptophan content. Thus it can be used as an alternative of tryptone. Tryptone Water is recommended by APHA (1) for detection of indole production by coliforms, which is a key feature in differentiation of bacteria. A slight modification of Tryptone Water (M463I) is recommended by ISO committee (4) for the same purpose. This test demonstrates the ability of certain bacteria to hydrolyze the amino acid tryptophan to indole mediated by suitable enzymes. Liberated indole gets accumulated in the medium (2). The indole produced can be detected by either Kovac's or Ehrlich's reagent (3). Indole combines with the aldehyde present in the above reagent to give red colour in the alcohol layer. The alcohol layer extracts and concentrates the red colour complex. Tryptone Water HiVeg® can be used in conjunction with Brilliant Green Bile HiVeg® Broth 2% (MV121) to determine the most probable number (MPN) of E.coli in food sample. Growth and gas production in MV121 and indole production in Tryptone water HiVeg® following incubation of both media at 44± 1°C is used as the basis for the presumptive E.coli test. For determination of indole, inoculate the medium with inoculum of an 18-24 hours pure culture. Incubate the tubes at 35± 2°C for 18-24 hours. Add 0.5 ml of indole reagent (R008) directly to the tube and agitate. Allow the tubes to stand for 5-10 minutes. Formation of red ring at the top of the tube indicates indole production. Indole testing is recommended as an aid in the differentiation of microorganisms based on indole production. For complete identification of the organisms, further biochemical confirmation is necessary.