Chromogenic culture media are culture media used to isolate, identify and differentiate specific microorganisms from a heterogeneous population. Chromogenic media contain colourless soluble molecules called chromogens.  Chromogens consist of two parts: a substrate (which is the target of the specific enzyme activity of the microorganism) and a chromophore. The chromogenic substrate which is used by the microorganism to give colored colonies specific to each microorganism. When the bond between the substrate and the chromophore is broken by a specific enzyme produced by the target microorganism, the chromophore is released. In its unconjugated form, the chromophore has a distinctive color. Due to its reduced solubility, the chromophore forms a precipitate that imparts a unique color to the colony. Depending on the color of the result, the presence or absence of the target organism is determined and also accurately differentiated from others. Chromogenic media may also contain inhibitors to make them selective for certain microorganisms and thus simplify the reading of results.