In the context of microbiology plating methods, what is a bacterial colony?

• A. A single bacterial cell observed under a microscope after staining
• B. A visible mass of microbial growth on solid medium that typically arises from a single cell or a small clump of cells (a colony-forming unit, CFU)
• C. A liquid culture containing a mixture of many bacterial species growing throughout the broth
• D. A sterile area of agar where bacterial growth has been completely inhibited by an antiseptic

Answer: (B)

Verified step by step guidance

1. Understand that in microbiology, a bacterial colony refers to a visible cluster of bacteria that grows on a solid nutrient medium, such as agar in a petri dish.
2. Recognize that each colony typically originates from a single bacterial cell or a small group of cells known as a colony-forming unit (CFU), which multiply to form the visible mass.
3. Differentiate a bacterial colony from other concepts: it is not a single cell observed under a microscope, nor is it a liquid culture or a sterile zone on agar.
4. Note that the colony's visibility is due to the dense growth of bacteria, which can be seen with the naked eye without the need for staining or microscopy.
5. Conclude that a bacterial colony is essentially a macroscopic growth representing the progeny of one or a few bacterial cells, useful for isolating and studying specific bacterial strains.