Katana VentraIP

Colony-forming unit

In microbiology, colony-forming unit (CFU, cfu or Cfu) is a unit which estimates the number of microbial cells (bacteria, fungi, viruses etc.) in a sample that are viable, able to multiply via binary fission under the controlled conditions. Counting with colony-forming units requires culturing the microbes and counts only viable cells, in contrast with microscopic examination which counts all cells, living or dead. The visual appearance of a colony in a cell culture requires significant growth, and when counting colonies, it is uncertain if the colony arose from one cell or a group of cells. Expressing results as colony-forming units reflects this uncertainty.

For the human hematopoietic cell, see Hematopoietic stem cell.

The pour plate method wherein the sample is suspended in a Petri dish using molten agar cooled to approximately 40–45 °C (just above the point of solidification to minimize heat-induced cell death). After the nutrient agar solidifies the plate is incubated.

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The spread plate method wherein the sample (in a small volume) is spread across the surface of a nutrient agar plate and allowed to dry before incubation for counting.

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The membrane filter method wherein the sample is filtered through a membrane filter, then the filter placed on the surface of a nutrient agar plate (bacteria side up). During incubation nutrients leach up through the filter to support the growing cells. As the surface area of most filters is less than that of a standard Petri dish, the linear range of the plate count will be less.

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The or drop-plate method wherein a very small aliquot (usually about 10 microliters) of sample from each dilution in series is dropped onto a Petri dish. The drop dish must be read while the colonies are very small to prevent the loss of CFU as they grow together.[12]

Miles and Misra methods

Colony-forming units are used to quantify results in many microbiological plating and counting methods, including:


However, with the techniques that require the use of an agar plate, no fluid solution can be used because the purity of the specimen cannot be unidentified and it is not possible to count the cells one by one in the liquid.[13]

OpenCFU is a program designed to optimise user friendliness, speed and robustness. It offers a wide range of filters and control as well as a modern user interface. OpenCFU is written in C++ and uses OpenCV for image analysis.[17]

free and open-source

NICE is a program written in that provides an easy way to count colonies from images.[18]

MATLAB

and CellProfiler: Some ImageJ macros[19] and plugins and some CellProfiler pipelines[20] can be used to count colonies. This often requires the user to change the code in order to achieve an efficient work-flow, but can prove useful and flexible. One main issue is the absence of specific GUI which can make the interaction with the processing algorithms tedious.

ImageJ

Cell counting

Growth medium

Miles and Misra method

Most probable number

Replica plating

Viral plaque

Fishman, William H.; Bernfeld, Peter (1955). . Methods in Enzymology. Vol. 1. pp. 262–9. doi:10.1016/0076-6879(55)01035-5. ISBN 978-0-12-181801-2.

[31] Glucuronidases