Plate Count Agar
Plate Count Agar - Related Videos
04:36
Assay for Adhesion and Agar Invasion in S. cerevisiae
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Cited by 17 •
2006
We describe a qualitative assay for yeast adhesion and agar invasion as a measure of invasive and pseudohyphal differentiation. This simple assay can be used to assess the invasive phenotype of various mutants as well as the effects environmental cues and signaling pathways on yeast differentiation.
02:15
Subculturing Sulfite-Reducing Anaerobic Bacteria from an Agar Culture
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2025
Source: Anwar, Z., et al. Enrichment and Detection of Clostridium perfringens Toxinotypes in Retail Food Samples. J. Vis. Exp. (2019).In this video, sulfite-reducing bacteria are cultured in a sulfite-containing agar medium, where they grow anaerobically and reduce sulfite to hydrogen sulfide, forming black precipitates with iron ions. Black colonies are isolated from the agar depth using aseptic techniques and transferred to fresh medium for continued anaerobic incubation.
03:37
Assessing the Antimicrobial Activity of Nisin Variants Using an Agar Well Diffusion Assay
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2025
Source: Nickling, J. H., et.al. Antimicrobial Peptides Produced by Selective Pressure Incorporation of Non-canonical Amino Acids. J. Vis. Exp. (2018)This video demonstrates an agar well diffusion assay used to evaluate the antimicrobial activity of nisin variants. It shows how Lactococcus lactis expressing the membrane-bound peptidase NisP activates nisin precursors produced in E. coli, resulting in growth inhibition halos. The size of these halos reflects the bioactivity of each nisin variant.
06:08
A Charcoal Agar Resazurin Assay to Evaluate Test Compound Activity Against Mycobacteria
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2025
This video showcases the Charcoal Agar Resazurin Assay (CARA) for evaluating the activity of antimicrobial compounds against Mycobacterium tuberculosis. CARA aids in assessing the efficacy of these compounds by gauging their impact on bacterial growth and distinguishing between bactericidal and bacteriostatic effects.
18:00
Aseptic Laboratory Techniques: Plating Methods
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Cited by 490 •
2012
When working with media and reagents used to culture microorganisms, aseptic technique must be practiced to ensure contamination is minimized. A variety of plating methods are routinely used to isolate, propagate, or enumerate bacteria and phage, all of which incorporate procedures that maintain the sterility of experimental materials.
FAQs
The solid agar matrix keeps the inoculated material localized while nutrients support multiplication of cells or cell clusters. As growth proceeds, each viable, culturable unit can produce a visible colony that serves as the basis for a colony-forming unit estimate. This physical separation makes individual colonies observable and countable rather than blending growth throughout a liquid sample.
Incubation conditions determine which microorganisms can grow well enough to form visible colonies. Consequently, the resulting count reflects organisms compatible with the selected conditions, not every microorganism present in the sample. Keeping conditions defined allows researchers to compare samples more meaningfully, while changing them can change recovery and therefore alter the apparent viable, culturable microbial load.
Serial dilution reduces the concentration of microorganisms introduced onto a plate, helping produce a number of colonies that can be counted. Surface-spread and pour-plate approaches place the diluted sample into the solid medium in different ways. Selecting an appropriate dilution and method supports clearer colony enumeration, whereas excessive or insufficient growth can make comparison of samples less useful.
An environmental sample is serially diluted, then inoculated onto Plate Count Agar using either a surface-spread or pour-plate approach. Plates are incubated under defined conditions until visible colonies develop, after which colonies are counted and used to estimate colony-forming units. Applying the same workflow across samples supports comparisons of microbial loads or changes over time.
Plate Count Agar can support viable, culturable microbial assessments in environmental materials such as water and soil, as well as in food and other environments. The resulting colony-forming unit estimates help quantify microbial loads, compare samples, and monitor changes in environmental quality. Interpretation should remain tied to the selected growth conditions because organisms unable to grow there are not represented.
A colony-forming unit estimate indicates the recoverable viable, culturable fraction under the assay's selected conditions. It should not be treated as a complete census of all microorganisms in water, soil, or another sample. The measure is most useful for comparing microbial loads between samples or tracking changes in environmental quality when dilution, plating approach, and incubation conditions are kept defined.