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Differential media are bacteriological growth media that contain specific ingredients to allow one to distinguish selected species or categories of bacteria by visual observation. Differential Media are used to distinguish between closely related organisms or groups of organisms. Differential media contain compounds that allow some groups of microorganisms to be visually distinguished by the appearance of the colony or the surrounding media. Due to the presence of certain dyes or chemicals in the media, the organisms will produce characteristic changes or growth patterns that are used for identification or differentiation. This macroscopic differentiation of bacteria is based on the capability of the bacteria to carry out specific biochemical processes. Blood agar is one type of differential medium, allowing bacteria to be distinguished by the type of hemolysis produced.