Bacterial Quantification
Bacterial Quantification - Related Videos
07:35
Preparation, Imaging, and Quantification of Bacterial Surface Motility Assays
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Cited by 68 •
2015
Swarming motility is influenced by physical and environmental factors. We describe a two-phase protocol and guidelines to circumvent the challenges commonly associated with swarm assay preparation and data collection. A macroscopic imaging technique is employed to obtain detailed information on swarm behavior that is not provided by current analysis techniques.
04:17
Quantification of Bacterial Alginate Using the Uronic Acid Carbazole Assay
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2025
Source: Al Ahmar, R., et al. Culture of Small Colony Variant of Pseudomonas aeruginosa and Quantitation of its Alginate. J. Vis. Exp. (2020)This video demonstrates a colorimetric assay to quantify alginate produced by Pseudomonas aeruginosa, using carbazole to detect uronic acids after acid hydrolysis. The method enables comparative analysis of alginate production normalized to bacterial biomass in research and clinical studies.
09:17
Quantification of Bacterial Histidine Kinase Autophosphorylation Using a Nitrocellulose Binding Assay
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Cited by 3 •
2017
We report and demonstrate an optimized nitrocellulose binding assay that can be used to quantify autophosphorylation of purified bacterial histidine kinases. Our method has several advantages over traditional SDS-PAGE based techniques, providing a valuable alternative for characterizing these important proteins.
03:52
Quantification of Bacterial Load in Mouse Spleen and Liver After Systemic Infection
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2026
Source: Ahn, J. J., et al. Experimental Infection with Listeria monocytogenes as a Model for Studying Host Interferon-γ Responses. J. Vis. Exp. (2016)The video demonstrates bacterial load measurement in spleen and liver tissues isolated from mice infected with an intracellular bacterial pathogen. Bacteria, accumulated within tissue-resident phagocytes during systemic infection, are released using detergent-based lysis and mechanical disruption. Serial dilutions of the homogenates are plated on...
02:23
Quantification of Light-Induced Bacterial Inactivation Through Reactive Oxygen Species Generation
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2025
Source: Cheng, C., et al. Inactivation of Pathogens via Visible-Light Photolysis of Riboflavin-5′-Phosphate. J. Vis. Exp. (2022).In this video, a buffered reaction mixture containing L-methionine, nitro blue tetrazolium (NBT), and flavin mononucleotide (FMN) is irradiated with violet light to induce reactive oxygen species (ROS) production. This leads to bacterial inactivation and the formation of spectrometrically detectable formazan.
FAQs
The distinction depends on what is being measured. Serial dilution followed by agar plating estimates viable cells through colony-forming units, because the counted colonies arise from cells capable of producing growth under the assay conditions. Optical density instead reflects culture turbidity and therefore provides an estimate of total biomass. Selecting between them determines whether the result emphasizes recoverable viable cells or overall culture material.
Optical density offers a rapid way to follow bacterial cultures because turbidity can be related to cell concentration. It is therefore useful when researchers need repeated measurements of population changes across time or conditions. However, it answers a different biological question from colony counting: the measurement represents total biomass rather than the number of viable cells recovered as colonies on agar.
When cultivation is difficult, quantitative PCR extends bacterial quantification beyond methods that depend on growth on agar. The assay measures bacterial DNA, providing a molecular estimate of the target population even when cultivation-based recovery is not practical. This makes it relevant to samples in which researchers need bacterial abundance information but cannot readily obtain it through standard culture-dependent counting.
Researchers serially dilute a culture, place dilution samples on agar, and count the resulting colony-forming units. The dilution step brings the population into a countable range, while agar provides the growth surface used to reveal colonies. Results can then be used to estimate the original bacterial abundance and compare cultures measured under the same workflow.
Researchers can measure the same population under different conditions or at multiple time points, then compare the resulting abundance estimates. Those comparisons reveal whether a bacterial population increases, decreases, or differs between environments or treatments. In biology, this approach supports growth studies and helps evaluate changes associated with contamination, infection-related investigations, or antibiotic activity.
Applications span environmental monitoring, food safety, infection biology, and studies of antibiotic activity. In each setting, bacterial quantification supplies a way to track population size or changes rather than relying only on descriptive observations. The selected readout can be matched to the research question: colony-forming units for viable-cell estimates, optical density for biomass, or quantitative PCR when cultivation is difficult.