Nitrate

Nitrate broth is created with beef extract, Peptone, and Potassium Nitrate. The media also includes a small inverted tube also filled with the broth called a Durham tube. The test checks for the various end products of Nitrate when it is reacted upon by the various tested bacteria. The three outcomes important here are of no reduction, reduction to nitrite, and reduction to Nitrogen gas. Nitrite has no more color to it than Nitrate so two reagents have to be added in order to see the change. These reagents are Sulfanilic Acid, which is converted to Diazotized Sulfanilic Acid in the presence of nitrite, and alpha-Naphthylamine which binds with the previous molecule to form a cherry red dye (p-Sulfobenzene-azo-alpha-naphthylamine). Nitrogen gas will form bubbles in the Durham tube visible to the naked eye. To really show that the Nitrate has been reduced, zinc has to be added into the broth. Zinc forcibly converts Nitrate to Nitrite, causing nothing in tubes that have used all the nitrate, but will cause inert result tubes to turn red from the already added reagents. This process may take a few minutes to fully take effect.