Differential and selective media are used extensively to differentiate between different groups, genera, and species of bacteria and will be used in almost all subsequent labs:

• A differential media contains biochemical substrates that mayor may not be utilized (or modified) by different bacteria. The utilization or modification of the substrate is usually indicated by a color change in the colony and/or surrounding bacteriological media. Examples of commonly used differential reactions are sugar utilization (with a pH indicator and possibly an inverted tube to trap gas) or enzymatic reactions (using a fluorescent substrate or clearing an added agent from solid media).