Positive indole control: Escherichia coli Negative indoloe control: Enterobacter aerogenes.
This is shown by a spreading turbidity from the stab line or a turbidity throughout the medium (compare with an uninoculated tube).
Urease production This is shown by a red-pink colour in the medium.
NITRATE REDUCTION TEST
This test is used to differentiate members of the Enterobacteriaceae that produce the enzyme nitrate reductase, from Gram negative bacteria that do not produce the enzyme.
The test is also helpful in differentiating Mycobacterium species as explained.
A heavy inoculum of the test organism is incubated in a broth containing nitrate. After 4 hours, the broth is tested fro the reduction of nitrate to nitrite by adding sulphanilic acid reagent. If nitrite is present, the acid reagent is diazotizex and forms a pink-red compound with alpha-naphthylamine. When nitrite is not detected it