Acetate agar is used for differentiation according to the ability to ferment acetate. Due to the fact that acetate in the medium composition is the sole source of carbon, bacterial growth, are not capable of disposal, is suppressed. Bacteria that fermented it in the course of their life produce an alkaline solution which changes the medium  color from green to blue. Samples cultured at 37 ° C, the final result is evaluated after 72 hours, although usually within 24 hours the reaction is already taking place. The duration of cultivation depends on the strain that you analyze.