What Is an Isolated Colony?

An isolated colony is a bacterial colony that has been isolated from other contaminants, usually by placing a sample in a sterile petri dish or glass slide with nutrients. This process ensures any observations or experiments are free from outside biological contaminants. This colony is often called a "pure culture."

Because the purest culture is derived from a single cell, biologists may go to great lengths to create isolated colonies. The first culture is considered contaminated. It is dispersed across the nutrient medium, often simply by streaking it across the slide or dish. If done correctly, this ensures that dividing cells will create small isolated colonies that can then be moved to another slide as a pure culture. Another method for creating pure cultures involves dissolving bacterial samples in water and then using a microscope to locate a droplet with a single isolated bacterium. This bacterium is then dropped into a water-nutrient solution to create the colony.

Once an isolated colony has been developed, it can be used for several purposes. In medical labs, isolated colonies are often used to identify and diagnose disease, examine the qualities of a cancer cell sample or determine what antibiotics are most efficacious in combating the bacterium. Genetics labs use these samples to experiment with recombinant DNA or to look for specific genes.