Bacterial Colony Enumeration
Bacterial Colony Enumeration - Related Videos
03:16
Processing of Infected Tissues for Bacterial Enumeration in a Mouse Co-Infection Model
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2026
Source: Lenhard, A., et al. A Mouse Model for the Transition of Streptococcus pneumoniae from Colonizer to Pathogen upon Viral Co-Infection Recapitulates Age-Exacerbated Illness. J. Vis. Exp. (2022)This video demonstrates the processing of lungs from a mouse co-infected with a pathogenic bacterium and a virus. Mincing, homogenizing, and plating the lung tissue allows quantification of bacterial load, indicating bacterial spread to the lungs and disease severity.
10:57
Culturing and Enumerating Bacteria from Soil Samples
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2023
Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - The University of Arizona Demonstrating Authors: Bradley Schmitz and Luisa Ikner Surface soils are a heterogeneous mixture of inorganic and organic particles that combine together to form secondary aggregates. Within and between the aggregates are voids or pores that visually contain both air and water. These conditions create an ideal ecosystem for bacteria, so all soils contain vast populations of bacteria, usually over 1 million...
10:53
Serial Dilutions and Plating: Microbial Enumeration
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2023
Source: Jonathan F. Blaize1, Elizabeth Suter1, and Christopher P. Corbo1 1 Department of Biological Sciences, Wagner College, 1 Campus Road, Staten Island NY, 10301 Quantitative assessment of prokaryotes can be onerous given their abundance, propensity for exponential proliferation, species diversity within a population, and specific physiological needs. Compounding this challenge, is the four-phase nature in which bacteria replicate (lag, log, stationary and death). The ability to accurately...
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.
FAQs
Serial dilution places the original sample into a range of concentrations, allowing colony counts to be related back to the starting material. Recording the dilution factor and plated volume is essential because the observed number of colonies represents only the portion deposited on agar. This adjustment makes bacterial burdens comparable across samples and experimental conditions.
The sample may be spread across an agar surface or incorporated through a pour-plate approach, and the resulting colonies must develop under suitable incubation conditions. These choices determine whether viable bacteria become visible for counting. Consequently, differences in agar handling or incubation conditions can affect the observed CFU value and the comparison between samples.
A colony-forming unit provides a countable measure linked to viable bacteria that produce visible colonies under the selected culture conditions. It therefore describes microbial burden rather than simply reporting the presence of bacterial material. In infection studies, this measurement supports quantitative assessment of bacterial growth, colonization, and changes produced by immune or therapeutic interventions.
A typical workflow begins with preparing serial dilutions of the sample, followed by transferring a measured volume onto or into agar. After incubation under suitable conditions, visible colonies are counted and the result is adjusted for both dilution and plated volume. Applying the same workflow across samples enables quantitative comparisons among experimental groups.
Researchers apply colony enumeration when they need to quantify pathogen colonization, bacterial growth, or the effects of immune defenses. It can compare infection outcomes across experimental conditions and assess whether antimicrobial treatments reduce microbial burden. The method also supports studies of genetic changes by measuring how altered bacterial or host conditions affect recoverable growth.
Adjusted colony counts provide a quantitative basis for comparing bacterial burdens between infected samples, treatment groups, or different experimental conditions. Higher or lower recoverable burdens can indicate differences in pathogen growth or control, while repeated comparisons help characterize infection severity and treatment effects. In immunology, the measurements connect immune defenses with changes in bacterial colonization.