An isolated colony is formed when:

• A. multiple bacterial species are mixed together in a liquid broth
• B. a colony is transferred from one plate to another using a sterile loop
• C. a single bacterial cell divides repeatedly on a solid medium
• D. bacterial cells are spread evenly across the entire surface of an agar plate

Answer: (C)

Verified step by step guidance

1. Understand the definition of an isolated colony: it is a visible cluster of microorganisms all originating from a single bacterial cell that has divided repeatedly on a solid medium.
2. Recognize that when multiple bacterial species are mixed in a liquid broth, colonies are not isolated because the bacteria are suspended and not separated on a solid surface.
3. Know that transferring a colony from one plate to another using a sterile loop is a method of inoculation, not the formation of an isolated colony itself.
4. Understand that spreading bacterial cells evenly across the surface of an agar plate is a technique to obtain isolated colonies, but the isolated colony itself forms when a single cell divides and grows into a visible cluster.
5. Conclude that the correct description of an isolated colony is when a single bacterial cell divides repeatedly on a solid medium, leading to a distinct, separate colony.