Plate Counts
Plate Counts - 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.
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...
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.
FAQs
The number of colonies observed depends on whether microorganisms can reproduce under the defined incubation conditions. Temperature, duration, and other culture conditions therefore shape the measured result, because only organisms capable of growth in that setting become visible colonies. Consistent conditions are important when comparing samples or evaluating changes in microbial concentration.
A colony-forming unit represents one or more cells that retain the ability to reproduce and produce a visible colony. Cells occurring together can therefore contribute to a single CFU rather than several separately counted colonies. Plate counts estimate reproductive units in the sample, not necessarily the exact number of individual cells present.
Serial dilution creates samples with progressively lower microorganism concentrations, increasing the chance that at least one plate will contain colonies suitable for counting. The selected colony number is then interpreted with the corresponding dilution factor to estimate the concentration in the original sample. This links the observed plate result to the starting material.
Plates with countable colony numbers provide a more practical basis for estimating viable microorganism concentration. Extremely crowded plates make individual colonies difficult to distinguish, while very sparse plates provide less observational information. Selecting an appropriate plate helps connect the visible colony total with the dilution factor and improves interpretation of the original sample.
After serial dilution, researchers place an aliquot of the diluted sample onto solid culture medium by spreading it across the agar or incorporating it through a pour-plating approach. The plates are then incubated under defined conditions, and visible colonies are counted. The chosen format is therefore part of how diluted samples are transferred for growth and measurement.
Plate counts provide an estimate of viable microorganism concentration, expressed through colony-forming units associated with the original sample. In biology, researchers can use these measurements to examine bacterial growth, compare microbial levels in environmental or water samples, assess food safety, and evaluate changes associated with antimicrobial treatments.
Researchers can compare viable microorganism estimates before and after an antimicrobial treatment by applying the same counting approach under defined culture conditions. A change in recovered CFUs indicates a change in microorganisms capable of reproducing under those conditions. This supports evaluation of treatment effectiveness while keeping dilution and incubation factors consistent.