Colony Count Procedure
Colony Count Procedure - Related Videos
03:55
Counting Colony Forming Units (CFUs): Quantifying Bacteria from Fly Bodies
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2023
Drosophila microbiota impacts the animal's development, immunity and physiology. This video describes a method to quantify bacteria from flies by determining the colony forming units from whole body preparations. The featured protocol demonstrates the technique with flies, reared under gnotobiotic conditions using four bacterial species.
11:01
Automated Quantification and Analysis of Cell Counting Procedures Using ImageJ Plugins
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Cited by 90 •
2016
This paper describes the quantification of hemocytometer and migration/invasion micrographs through two new open-source ImageJ plugins Cell Concentration Calculator and migration assay Counter. Furthermore, it describes image acquisition and calibration protocols as well as discusses in detail the input requirements of the plugins.
06:44
Keratinocyte Colony Formation Assay: An In Vitro Assay to Assess the Ability of Keratinocytes to Grow into Colonies
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2023
In this video, we perform a clonogenic assay of keratinocytes harvested from adult mice to determine the ability of individual cells to proliferate and form colonies. This keratinocyte harvesting technique is useful for studying other downstream aspects of cutaneous chemical carcinogenesis and tumor promotion.
12:55
Fast Colony Forming Unit Counting in 96-Well Plate Format Applied to the Drosophila Microbiome
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Cited by 5 •
2023
This method quantifies microbial abundance using a 96-well plate format to plate colony forming units (CFUs) and is applied to the Drosophila microbiome in whole fly homogenate samples. CFUs are counted with an automated image analysis software provided here.
10:19
Using a Hemacytometer to Count Cells
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2023
Many biomedical experiments require manipulation of a known quantity of cells, in order to achieve accurate, reproducible, and statistically-relevant data. Therefore, learning how to count cells is a particularly essential technique for any successful biomedical scientist. The most common way to count cells is by using a hemacytometer - an instrument that bears two laser-etched grids, which aid in the enumeration of an aliquot cells under a simple light microscope. This data can then be used to...
FAQs
CFU captures viable colony-producing units, not necessarily individual cells. A visible colony can originate from one living microorganism or from a cluster that remains together during processing. Consequently, the reported value estimates the number of units capable of forming colonies under the selected culture conditions. This distinction matters when comparing microbial burden between infection samples or treatment groups.
Serial dilution controls crowding on the agar surface and makes colonies easier to distinguish. If a dilution is too concentrated, overlapping growth can obscure colonies; if it is too dilute, few colonies may be available for a useful estimate. Selecting a countable dilution and applying the same dilution logic across samples improves the reliability of CFU comparisons.
Medium composition and incubation conditions determine which viable microorganisms can produce visible colonies. A suitable agar medium, together with defined incubation conditions, is therefore part of the measurement rather than a minor technical detail. Changes in these factors can alter colony recovery and visibility, so samples should be evaluated under consistent culture conditions when growth or treatment effects are compared.
Standardization should cover specimen dilution, the measured volume placed on agar, the selected medium, incubation conditions, and the dilution used for counting. Accuracy at each stage affects the final CFU estimate, so the same workflow should be applied across experimental groups. This consistency allows differences to be interpreted as biological or treatment-related rather than procedural.
Researchers can compare CFU estimates from treated and untreated samples to assess changes in recoverable microbial burden. A lower count after treatment is interpreted in relation to the same culture and dilution conditions, because recovery also depends on those variables. In infection studies, this approach helps quantify treatment effects while preserving a direct connection to viable microbial growth.
By quantifying recoverable microorganisms, the procedure provides an outcome for studying bacterial growth and the effects of host immune defenses. Samples collected under different experimental conditions can be compared when dilution, agar, incubation, and counting practices are standardized. The resulting CFU measurements help connect immune or infectious processes with changes in microbial burden.