Nitrate Reduction Test 1
The purpose of this test is to determine whether an organism can reduce nitrate to nitrite or free nitrogen gas. After incubation, sulphanilic acid and alpha-naphthole are added. If the nitrate has been reduced to nitrites by the organism, a diazonium compound is formed, colouring the medium red. If the nitrate has not been reduced or if it has been reduced to free nitrogen gas, the broth remains colourless. To differentiate between these two, zink dust is added. This catalyses the reduction of nitrate in the broth to nitrite, which then allows the formation of the diazonium compound with resulting red colour. If the organism has reduced the nitrate to free nitrogen gas then the medium will remain colourless. Positive result: Nitrate reduced either to nitrite or nitrogen gas. Negative result: Nitrate has not been reduced. 1. Uninoculated medium. 2. Positive reaction after addition of sulphanilic acid and alpha-naphthole: Escherichia coli 3. Colourless after addition of sulphanilic acid and alpha-naphthole: Acinetobacter 4. Negative reaction. Red (lighter than the reaction in tube 2) colour after addition of the zink dust due to the reduction of nitrate still in the medium to nitrite: Acinetobacter
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