Pigments can be divided into two basic types: water insoluble and water soluble. If the pigment is water insoluble, as in the case of most chromogenic bacteria, it does not diffuse out of the organism. As a result, the colonies are pigmented but the agar remains the normal color. If the pigment is water soluble (as in the case of Pseudomonas aeruginosa) it will diffuse out of the organism into the surrounding medium. Both the colonies and the agar will appear pigmented.

State the color of the pigment (red, orange, green, etc.) and its solubility (water soluble or water insoluble).

Gary E. Kaiser, Ph.D.
Professor of Microbiology
The Community College of Baltimore County, Catonsville Campus
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