ChromoGel - Chromogenic media are microbiological growth media that contain enzyme substrates linked to a chromogen (color reaction). The enzyme substrates, e.g. ONPG, CPRG, and MUG are organism specific or where they are not, the target organism is selected for by suppression of competing microflora. Chromogenic media are available as dehydrated bulk powder. They are also available in ready-to-use formats, and ’convenience’ packs.