In microbiology, colony-forming unit (CFU) is a measure of viable bacterial numbers. Unlike in direct microscopic counts where all cells, dead and living, are counted, CFU measures viable cells. A sample is spread or poured on a surface of an agar plate, left to incubate and the number of colonies formed are counted. CFU is not an exact measure of numbers of viable cells, as a colony-forming unit may contain any number of cells. An agar plate streaked with microorganisms Microbiology is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. ... This article does not cite its references or sources. ... This article or section does not cite its references or sources. ...