Agar Plate Enumeration
Agar Plate Enumeration - Related Videos
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...
09:57
Visualization of the Charcoal Agar Resazurin Assay for Semi-quantitative, Medium-throughput Enumeration of Mycobacteria
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Cited by 10 •
2016
The charcoal agar resazurin assay (CARA) is a semi-quantitative, medium-throughput method to assess activity of test agents against mycobacteria that are replicating, non-replicating, or both. The CARA permits rapid evaluation of time- and concentration-dependent activity and identifies parameters to pursue by colony forming unit (CFU) assays.
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...
09:29
Algae Enumeration via Culturable Methodology
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2023
Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - The University of Arizona Demonstrating Author: Bradley Schmitz Algae are a highly heterogeneous group of microorganisms that have one common trait, namely the possession of photosynthetic pigments. In the environment, algae can cause problems for swimming pool owners by growing in the water. Algae can also cause problems in surface waters, such as lakes and reservoirs, due to algal blooms that release toxins. More recently, algae...
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.
FAQs
A visible colony is best interpreted as a colony-forming unit (CFU), because it may originate from one cell or from a cluster of cells that reproduced together. Consequently, the result estimates viable microorganisms in the tested sample rather than providing an exact direct cell count. This distinction matters when comparing microbial burden across infection or treatment conditions.
Serial dilution creates a set of sample concentrations, allowing the investigator to apply progressively smaller inocula to agar and identify a plate count that can be quantified. This step connects the number of colonies observed with the original sample through the dilution performed. It is therefore essential for converting growth on plates into an estimate of viable microbial abundance.
Incubation must be matched to the target organism because colony formation depends on conditions suited to that organism. If the selected conditions do not support its growth, the resulting count may not represent the microorganisms present in the sample. In infection research, consistent incubation conditions are therefore important when comparing bacterial survival, burden, or treatment-associated changes.
Comparisons are most meaningful when the dilution approach, plating format, incubation conditions, and colony-counting procedure are applied consistently. Samples can be spread or poured onto agar, but differences in how they are handled may affect the observed colony recovery. Standardizing these stages helps ensure that changes in CFU reflect the samples rather than the workflow.
Counts provide a practical measurement of viable bacteria in a sample, allowing researchers to assess whether microbial burden is higher or lower under different infection-related conditions. Because the readout reflects organisms capable of producing colonies under the selected growth conditions, it links experimental treatment or host-defense effects to recoverable microbial viability.
Researchers can compare CFU measurements from samples exposed to an antimicrobial intervention or host-defense condition with measurements from a relevant comparison sample. A difference in colony recovery indicates a change in viable microbial burden under the tested conditions. The approach therefore provides a quantitative outcome for evaluating how these factors affect microbial survival.