Bacterial Counting
Bacterial Counting - Related Videos
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.
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...
05:47
Counting and Determining the Viability of Cultured Cells
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Cited by 19 •
2008
Determining the number of cells in culture is important in standardization of culture conditions and in performing accurate quantitation experiments. In this video, we demonstrate how cells are counted using a hemacytometer.
06:37
Counting Human Neural Stem Cells
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Cited by 14 •
2007
Knowledge of the exact number of viable cells is required for many tissue culture manipulations. This protocol describes how to differentiate between live and dead cells and quantify cells using a hemacytometer. Although it describes counting human neural stem/precursor cells (hNSPCs), it can be used for other cell types.
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.
FAQs
The methods can produce different values because they detect different properties. Optical density estimates the signal from material in the culture and therefore includes living and dead cells, while agar-based colony formation records only cells capable of reproducing under the selected culture conditions. Microscopic counting provides a direct cell estimate, offering a separate comparison with these indirect or viability-dependent measurements.
The result of a colony-based count depends on whether cells can reproduce under the selected culture conditions. A bacterium present in the sample may therefore be absent from the resulting colony count if those conditions do not support its reproduction. This makes the measurement useful for estimating culturable, reproducing bacteria, but not necessarily total cells in the original sample.
Microscopic counting provides a direct way to estimate cells in a sample rather than relying on turbidity or colony formation. That distinction matters when researchers need an abundance measurement independent of whether cells produce colonies under chosen culture conditions. In comparative experiments, microscopy can therefore complement optical-density and agar-based measurements rather than serve as an interchangeable substitute.
To obtain a colony-based estimate, researchers serially dilute the bacterial sample and use the diluted material with agar so that growth produces colonies. The resulting colony number is interpreted in relation to the dilution used, allowing the original sample's bacterial concentration to be estimated. This workflow connects observed colony formation with the concentration of the starting sample.
The choice depends on the property being measured. Optical density is appropriate when the culture's overall turbidity is relevant, whereas colony formation is more informative when the focus is on bacteria capable of reproducing under specified culture conditions. Microscopy supplies a direct cell estimate. Matching the method to the question prevents unlike measurements from being treated as equivalent.
In biology, counts support growth-curve analysis, contamination monitoring, antibiotic studies, food and water safety testing, and biotechnology workflows. They also help standardize experimental cultures so that comparisons begin with a measured bacterial amount. Because each method captures a different aspect of abundance, researchers can select counts that fit the biological question and interpret outcomes within that measurement context.