Publish Time: 2022-12-14 Origin: Site
In microbiology,a colony forming unit (CFU, cfu, or Cfu) is a unit for estimating the number of viable microbial cells (bacteria,fungi,viruses,etc.) in a sample, capable of multiplying by binary fission under controlled conditions.Use Colony Counting the forming units requires culturing the microorganism and counting only live cells,in contrast to microscopy,which counts all live or dead cells.The visual appearance of a colony in cell culture requires significant growth,and when counting colonies,it is uncertain whether the colony is from a single cell or 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:
The pour plate method, in which samples are suspended in petri dishes using molten agar cooled to approximately 40-45 °C (just above freezing point to minimize heat-induced cell death).Plates were cultured after the nutrient agar had solidified.
Spread Plate method,in which the sample (small volume) is spread on the surface of a nutrient agar plate and allowed to dry before the cultures are counted.
Membrane filtration,where the sample is filtered through a membrane filter,which is 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 the plate count will be less.
The Miles and Misra method or the drop plate method,in which very small aliquots (usually about 10 microliters) from 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 because the purity of the specimen cannot be determined and individual cells in the liquid cannot be counted.
Colony counting is traditionally performed manually using a pen and click counter.This is usually a simple task, but can become very laborious and time-consuming when many boards must be enumerated.Alternatively, semi-automatic (software) and automatic (hardware + software) solutions are available.