CFU

In microbiology, a colony-forming unit is a unit which estimates the number of microbial cells in a sample that are viable and able to multiply via binary fission under the controlled conditions. Determining colony-forming units requires culturing the microbes and counting only viable cells, in contrast with microscopic examination which counts all cells, living or dead. The visual appearance of a colony in a cell culture requires significant growth, and when counting colonies, it is uncertain if the colony arose from a single cell or a group of cells. Expressing results as colony-forming units reflects this uncertainty.