A colony forming unit (CFU) is a measure of individual bacteria or fungi that are viable in a sample, therefore able to produce colonies. It quantifies the number of microbial cells that can grow visibly under defined conditions of energy (carbon) sources. Scientists use this measure to determine the number of viable cells in a known volume of a sample. As an example, if 1mL of a sample is spread onto a petri-dish containing nutrients, aminoacids, and minerals that are essential for bacteria and fungal growth, the resulting number of colonies would reflect the CFU/mL in the original sample. If the original sample were highly concentrated, a scientist may dilute it by a known factor before spreading it onto a petri dish to determine CFU. In this case, the scientist would perform calculations to determine CFU in the original sample. Here is an equation that could be used for this purpose: CFU in original concentrated sample = number of colonies from diluted sample × dilution factor.
A Colony Forming Unit (also known as CFU or cfu) is a measure commonly used in microbiology to determine the number of bacteria (or fungi) present in a sample that have the ability to multiply under controlled growth conditions.
If someone wishes to know the number of microorganisms present in a sample, one way would be to count all the microorganisms under a microscope. However, this would be time-consuming. An easier way is to dilute the sample and spread a small aliquot on a petri dish. Given suitable growth conditions, the microorganisms will grow into a number of small colonies. Assuming that each colony was formed from a single viable microorganism, we can estimate the total number of microorganisms present in a sample.
For example, 100 colonies are counted on a petri dish made by spreading 1 ml of a sample that was obtained after diluting the original sample in a 1:100 ratio. In such a case, the original sample contains 10,000 (= 100 x 100) microorganisms per mL or 10,000 CFUs per mL.
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