Author: Site Editor Publish Time: 2022-12-15 Origin: Site
In microbiology, a colony forming unit (CFU, cfu, or Cfu) is a unit used to estimate the number of viable microbial cells (bacteria, fungi, viruses, etc.) in a sample, capable of multiplying by binary fission under controlled conditions. Enumerating colony-forming units using colony-forming units requires culturing the microorganism and counting only living cells, as opposed to microscopy techniques, which count all living or dead cells.The visual appearance of colonies in cell culture requires obvious growth, and when counting colonies, it is uncertain whether the colonies are from a single cell or from a group of cells.Expressing the results as colony forming units reflects this uncertainty.
Colony forming units are used to quantify the results of many microbial plating and enumeration methods, including:
For the inverted plate method, samples are suspended in petri dishes using molten agar cooled to approximately 40–45 °C (just above freezing to minimize heat-induced cell death) Plates were cultured after the nutrient agar had solidified.For the plating method, samples (small volumes) are spread on the surface of nutrient agar plates and allowed to dry before counting cultures.Membrane filtration, where the sample is filtered through a membrane filter and then placed on the surface of a nutrient agar plate (bacteria side up).During incubation, nutrients seep through the filter to support the growing cells. Since most filters have a smaller surface area than a standard Petri dish,the linear range of plate counts will be less.The Miles and Misra method or the drop plate method, in which very small aliquots (usually about 10 microliters) of each serial dilution are dropped onto a Petri dish.The drip tray must be read when the colonies are very small to prevent the loss of CFU as they grow together.However, techniques that require the use of agar plates cannot be used with liquid solutions, as the purity of the specimen cannot be determined, nor can individual cells in liquid be counted.
Colony Counting Tool
Colony counting is traditionally performed manually using a pen and click counter.This is usually a simple task, but when many boards must be enumerated it can become very laborious and time consuming. Alternatively, semi-automatic (software) and automatic (hardware + software) solutions are available.