Colony Forming Units (CFU) Reviews

Things to know about colony-forming units

In microbiology, CFU is the abbreviation of the colony-forming unit. The unit is generally found on those products that consist of probiotics. This unit also measures the number of good bacteria and yeast inside the product.

A colony of yeast or bacteria indicates individual cells of one organism that grows in a well-balanced manner in masses. Speaking about molds, a colony refers to the group of filaments of similar mold that grows together. These units let you know the number of living microbes that remain present in a sample.

Microbiologists make use of the term CFU for describing the total number of live and active microorganisms in lieu of the inactive and dead bacteria. Scientists consider the viable organisms as probiotics. Viable refers to those microbes that have the capacity to remain alive under right circumstances.

In these days, probiotics are becoming increasingly common due to the adequate number of beneficial bacteria present in them. One can see the count of colony forming units on the packaging of the probiotic supplements.

Colony Forming Units Theory

Experts do plate counting for estimating the number of cells which is present in a sample. The plate counting is done on the basis of capability of giving rise to different colonies. The process is accomplished under different conditions of time, temperature and medium of nutrients.

One viable cell is capable of giving rise to one entire colony by the process of replication. There are several bacteria such as Staphylococcus and streptococcus that are capable of growing in chains.

The assessment of the number of microbes by the count of Colony Forming Units aids in undercounting the total number of living cells in one sample. This is the reason why the Colony Forming Unit count presume that each one of the colony is independent.

For E.Coli, the plate count ranges from 30 to 300 Colony Forming Units on a petri dish of standard size. To make sure whether a sample contains CFU in the above-mentioned range, experts dilute the sample. They also perform plating of different dilutions for the purpose. Generally, they perform 10 fold of dilutions for the purpose.

The experts accomplish the dilution series in 2 to 3 replicates from the selected dilution range. It is possible to read the Colony Forming Units count from the plate within a linear range. One advantage of undertaking this procedure is that varied species of microbes has the ability to give rise to colonies.

They are distinguished from one another macroscopically and microscopically. The colony morphing is highly beneficial for the identification of microorganisms that are present.

Colony Forming Units Uses

Microbiologists primarily use colony forming units for quantifying the results present in several plating of microbiology and methods of counting. Some of the other uses of these colony forming units are listed below:

Colony Forming Units are used in the Pour Plate method. In this procedure, the experts suspend the sample in a petri dish at a temperature of 40 to 45C. They make use of molten agar for suspension of the sample. After the solidification of nutrient agar, they incubate the plate.

Experts make use of Colony Forming Unit in Membrane Filter Method. Microbiologists filter the sample with the aid of a membrane filter. They place the filter on the nutrient agar plate surface. While accomplishing the incubation process, the nutrients leach via the filter for supporting the growing cells.

Since the filter surface area is less than that of the Petri dishes, the plate count will be lesser.

In the drop-plate method, the experts drop a small quantity of sample from every dilution on a petri dish. They read the drop dish when the colonies are quite small. They do this for preventing the CFU loss.

CFUs are used in the Spread Plate method as well. The experts spread a small quantity of the sample on the  nutrient agar plate surface. After this, the allow the same for drying followed by incubation required for counting.

Software for counting Colony Forming Units

It is possible to enumerate the colonies from the pictures of plates with the aid of software tools. The experts take images of the individual plate they should count. After which, they do analyze of the picture via a webcam or a digital camera. It does not take more than 10 seconds for taking a picture. On the other hand, it takes a lot of time for counting the Colony Forming Units in a manual way. It also helps in extracting other variables which include the color and size of the colonies.

OpenCFU: It is an open-source and free program that is designed for optimizing the robustness, speed and user friendliness. It imparts a vast range of control, filter, and a modern user interface.

NICE: This MATLAB written program renders an easy option for counting the colonies from the pictures.

ImageJ and CellProfiler: A few CellProfiler pipelines, ImageJ macros can assist in counting colonies. The user should be changing the code more often for achieving the efficient flow of work.

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