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Isolated Colonies
What is an isolated colony?
When you inoculate your media, you introduce bacterial cells into a nutrient-rich environment. The objective is to encourage those bacterial cells to divide and multiply their numbers.
Ideally, in the lab, you will usually be provided with pure cultures. However, when performing experiments such as your mixed unknown, you will need to be able to isolate each of the organisms present in your sample. The easiest and best way to do this is to streak for isolation .
When we streak for isolated colonies, we dilute our inoculum by streaking it across the agar. Our intent is to get the inoculum diluted to the point where there is only one bacterial cell deposited every few millimeters on the surface of the agar plate. When these lone bacterial cells divide and give rise to thousands and thousands of new bacterial cells, an isolated colony is formed.
Ideally, an isolated colony of bacteria is the progeny of a single bacterial cell. However, a colony-forming unit may also be a pair, a chain, or a cluster of cells.