∞ generated and posted on 2016.12.15 ∞
A single cell or group of cells that upon plating in or on solid media replicates to form a visible as well as well-defined area of growth.
| One uses the term Colony-Forming Unit rather than 'cell' or 'organism' to explicitly acknowledge the ambiguity of using the latter terms in a singular form since as a consequence of clumping or existence as cellular arrangements a 'unit' which is able to form a colony may in fact not consist of a single cell or single organism but instead more than one such entity physically stuck together. |
A colony can form starting with any number of cells and that the resulting colony will look pretty much the same unless it was started with an extremely large number of cells. In any case, the cells from which the colony is initiated would be found more or less of at the center of resulting colony. We thus employ the term colony-forming unit to describe the colony-forming cells because we can't be sure, from looking at the colony, that it was initiated with one versus many initial cells.
Figure legend: Illustration of how a colony can form, starting with any number of cells (left), and that the resulting colony will look pretty much the same (right) unless it was started with an extremely large number of cells. In any case, the cells from which the colony is initiated would be found, at the start of colony formation, more or less at the center of resulting colony. We thus employ the term colony-forming unit (a.k.a., CFU) to describe the colony-forming cells because we can't be sure, from looking at a colony, that it was initiated with one versus many initial cells.
See equivalently plaque-forming unit or PFU, where a plaque can be initiation with a single virus, aggregated virions, or a virus-infected cell or cells. See as well the concept of viable count.