One or more aggregated viable particles can be counted as one unit. When a number of VUs, known as colonies, are formed on the culture medium, they are usually written as CFU.

【Reference】 Microorganisms are organisms with a simple structure, a wide distribution, rapid reproduction, and the smallest individual size. The main types of microorganisms are bacteria, fungi (including molds and yeasts), actinomycetes, spirilla, rickettsiae, mycoplasmas, and viruses.

【Reference】 Since individual bacteria are invisible, certain means must be used to collect the bacteria into a culture dish containing a nutrient-rich culture medium, where, under specified conditions, the single individuals are cultured and multiplied into colonies (populations) visible to the naked eye and then counted. This number is the CFU.

【Reference】 By this method of forming colonies through culturing, the number of live bacteria with reproductive capability among the captured bacteria can be counted; only this quantity has biological significance.