Citrate

A green media that is made with sodium citrate (carbon source), ammonium phosphate(,Nitrogen source), and bromthymol blue (Dye, green in low pH, blue at high pH). This media tests for the presence of Citrase, which converts citrate into oxaloacatate, which can be processed by cells for energy or construction material. None of these byproducts are the end result for the visible test change. As the organism grows, it has to use ammonium phosphate and will slowly raise the pH of the media turning it blue. This blue color is the positive result, and the green color acts as the negative result.