Colony-forming unit
As colony forming unit ( CFU or CFU , English colony forming unit , CFU ) are called single or multiple contiguous individuals of microorganisms which, by their multiplication in or on a gel growth medium, a colony form. In the method for quantifying living microorganisms, this quantity is referred to by the abbreviation CFU or CFU.
method
Microorganisms can be quantified using cultural methods , e.g. B. by a surface-viable count or a plaque assay . In this case, usually a sample of material, the level of microorganisms is to be determined, on the surface of a culture medium - gel distributed as evenly as possible, or in the culture medium gel, individually so that, ideally, all individuals of the microorganisms or enough to be far apart and at appropriate Culture conditions form a colony visible to the eye through growth and multiplication. Under these ideal conditions, the number of colonies is equal to the number of individuals contained in the sample. In fact, under real conditions, some individuals can be so close together that they only form a single common colony, and some individuals often adhere so tightly to one another that they are not separated and only one colony develops from them. Under real, non-ideal conditions, the number of colonies is less than the number of individuals contained in the sample. That is why the term colony-forming unit was introduced, which corresponds to both individual individuals and several individuals who adhere to one another or lie close together.
A special feature of the method to quantify microorganisms with the help of a culture and by determining the number of colony-forming units is that the choice of culture conditions (culture medium, temperature, oxygen availability and the like) in microorganism societies with species that have different demands on the Establish culture conditions, often only a selection of all microorganisms occurring is recorded. This can be advantageous if only certain physiological types of microorganisms are to be recorded. This is disadvantageous when a so-called total germ count is to be determined in a mixed microorganism society, i.e. the number of all microorganisms contained.
See also
Web links
swell
- Andreas Paetz: Dictionary environmental investigation: terms, definitions and explanations from the areas of waste, soil, water . Beuth Verlag, 2011, ISBN 3-410-17127-4 , pp. 157 .