Question

Questions:

1. For a positive test result in Simmons Citrate media, explain why nitrogen metabolism is dependent on citrate metabolism.

2. Explain why nitrate metabolism is necessary for a positive result occurring and how a positive result is visualized.

Answer 1

Simmons citrate agar is the type of test media which tests the ability of the organism to utilize citrate as a carbon source. It contains sodium citrate which is the sole source of carbon, ammonium dihydrogen phosphate which is the sole source of nitrogen, other nutrients, and the pH indicator bromthymol blue.

1) For a positive test result in Simmons Citrate media, nitrogen metabolism is dependent on citrate metabolism because citrate is used as a carbon and energy source and the organism which has the capability to breakdown citrate produces alkaline carbonates and bicarbonates. In addition, ammonium hydroxide is produced when the ammonium salts in the medium are used as the sole nitrogen source.

2) This is because the carbon dioxide that is released reacts with water and the sodium ion in the medium to produce sodium carbonate which is an alkaline compound that raises the pH. In addition, ammonium hydroxide is produced when the ammonium salts in the medium are used as the sole nitrogen source. The citrate utilization produces an alkaline carbonate which results in a deep blue color change within the agar.