Urea Indole Broth ISO

L-Tryptophan is an essential amino acid and is converted to skatole and indole. Sodium chloride maintains the osmotic balance. Potassium phosphates act as a buffer system. Urea is a source of nitrogen for those organisms producing urease. Phenol red is the pH indicator.

This medium is recommended for the presumptive identification of Yersinia enterocolitica.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 30 grams of the medium in one liter of distilled water. Mix well. Add 10 mL of 95% ethanol. Dispense in 1-5 mL amounts into sterile tubes. AVOID OVERHEATING. DO NOT AUTOCLAVE.

If desired, add 2 g/L of agar for the detection of bacterial motility.

Instructions for use

1. Prepare a heavy suspension of the organism isolated from plated media.
2. Inoculate the Urea Indole Broth tubes.
3. Incubate at 35 ± 2 °C for 18-24 hours.
4. Observe at 3-4 hours for any positive urease in tubes that turn the indicator a deep violet red color (alkalinization), typical of Proteus or Yersinia. Klebsiella and some Citrobacter develop positive tubes after 18 hours.
5. Indole production is determined by adding a few drops of Kovac's Reagent (LC-5205). A positive test is indicated by the development of a red color in the reagent layer.
6. Tryptophan deaminase (TDA) is demonstrated by adding to a 24 hours culture a few drops of a 30% solution, diluted 1:3, of iron perchloride. The appearance of a brown or red-brown color indicates a positive TDA.
7. For the presumptive identification of Yersinia enterocolitica, inoculate and incubate at 30 °C for 24 hours. If the medium is not inoculated with a sufficient quantity of inoculum, it is possible to find false negatives.

• Roland F. Bourbon D, Sztrum S. Ann. Inst. Pasteur, 73. 914-916.
• ISO 10273:2003 Microbiology of food and animal feeding stuffs - Horizontal method for the detection of presumptive pathogenic Yersinia enterocolitica.