Bacterial Colony Counting
Bacterial Colony Counting - 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.
09:59
Community DNA Extraction from Bacterial Colonies
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2023
Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - The University of Arizona Demonstrating Author: Luisa Ikner Traditional methods of analysis for microbial communities within soils have usually involved either cultural assays utilizing dilution and plating methodology on selective and differential media or direct count assays. Direct counts offer information about the total number of bacteria present, but give no information about the number or diversity of populations present...
03:54
Preparation of Bacterial Biofilm Colonies for Morphological Analysis
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2026
Source: Bucher, T., et. al., Methodologies for Studying B. subtilis Biofilms as a Model for Characterizing Small Molecule Biofilm Inhibitors. J. Vis. Exp.(2016)This video demonstrates the preparation of mature bacterial biofilm colonies for high-resolution imaging. It covers fixation, dehydration, mounting, and metal coating steps to preserve and visualize biofilm morphology.
13:06
Solubilization and Bio-conjugation of Quantum Dots and Bacterial Toxicity Assays by Growth Curve and Plate Count
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Cited by 7 •
2012
Nanoparticles such as semiconductor quantum dots (QDs) can be used to create photoactivatable agents for anti-microbial or anti-cancer applications. This technique shows how to water-solubilize cadmium telluride (CdTe) QDs, conjugate them to an antibiotic, and perform a bacterial inhibition assay based upon growth curves and plate count.
02:25
Photodegradable Hydrogel-Based Isolation of Bacterial Colonies in Microwell Arrays
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2025
Source: Fattahi, N., et al. Photodegradable Hydrogel Interfaces for Bacteria Screening, Selection, and Isolation. J. Vis. Exp. (2021)This video demonstrates the use of photodegradable hydrogels to isolate bacterial colonies within silicon microwell arrays. Bacterial cells are first loaded into microwells, encapsulated in a crosslinked hydrogel, and cultured into distinct colonies. Upon exposure to ultraviolet light, targeted degradation of the hydrogel enables selective extraction of individual...
FAQs
Serial dilution places samples across a range of concentrations, increasing the likelihood that at least one plated dilution produces colonies suitable for counting. Without dilution, dense growth can make individual colonies difficult to distinguish. The resulting countable plate provides the basis for estimating the original sample’s viable bacterial load.
A colony-forming unit does not necessarily represent one independent bacterial cell. A visible colony may arise from a single viable cell or from a cell cluster that remains together during plating and growth. Consequently, the reported value estimates viable units capable of producing colonies, which is important when comparing samples or calculating infection burden.
Both approaches place diluted material onto or within solid agar so viable cells or clusters can develop into visible colonies. The choice identifies how the sample is physically combined with the medium, while the central interpretation remains a colony-based estimate. Using the same approach across samples supports consistent comparisons.
Use the same dilution sequence, plating approach, incubation conditions, and counting procedure for samples intended for comparison. After incubation, record colonies on the selected plates and use those observations to calculate colony-forming units for the original samples. Consistency supports meaningful comparisons between experimental groups and reduces variation caused by the measurement process.
It can quantify bacterial survival before and after antimicrobial treatment, allowing investigators to assess whether treatment conditions are associated with lower recoverable growth. The same measurement framework supports comparisons of treatment effectiveness across experimental samples. Because the readout concerns viable bacteria, it helps determine whether organisms remain capable of producing colonies.
In host-pathogen experiments, counts provide a quantitative infection-related outcome for testing how immune cells or other host conditions influence bacterial growth. Investigators can compare bacterial burden among experimental groups and relate those differences to pathogen survival, treatment response, or changing host conditions. This connects microbiological measurement with research in immunology and infection.