Bacteria are inoculated on a medium containing sodium citrate and a pH indicator such as bromothymol blue.
The medium also contains inorganic ammonium salts, which are utilized as sole source of nitrogen.
This results in a change of the medium's color from green (neutral) to blue (alkaline).
Bacterial colonies are picked up from a straight wire and inoculated into slope of Simmons citrate agar and incubated overnight at 37 °C.
If the organism has the ability to use citrate, the medium usually changes its color from green to blue, though growth on the medium even without colour change is considered a positive result.