🔬 Soft-Agar Overlay

Means of plating that involves two layers of media, one consisting of hard or bottom agar that serves as a base and the other consisting of soft or top agar which is poured over the base.

by Stephen T. Abedon Ph.D. Steve Abedon, Ph.D., has taught well over 100 individual classes and ~10 individual courses (including introductory biology, microbiology, physiology, biochemistry, etc.) over his 30+ years as a college professor. He has over 150 publications, including multiple monographs, and is ranked in the top 1 or 2 percent among researchers of all disciplines worldwide. His research focuses on bacteriophage biology and phage therapy. (abedon.1@osu.edu)

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About this entry: Soft-Agar Overlay is one of a growing set of phage biology and phage therapy terms defined here. For more phage terms, see Abedon, S.T. (2025). Phage Therapy Annotated Glossary. Preprints.org. 10.20944/preprints202508.0347.v1
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phage.org/terms/soft_agar_overlay.html  ·  Abedon’s Books  ·  DOI: 10.5281/zenodo.20173633

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Soft-Agar Overlay: Means of plating that involves two layers of media, one consisting of hard or bottom agar that serves as a base and the other consisting of soft or top agar which is poured over the base.

Discussion

The soft agar overlay method is the most common means by which phage plating and subsequent plaque formation is accomplished. Double overlay plaquing method can serve as a synonym and see by contrast direct-plating plaquing method.

For additional discussion and references, see Kropinski et al. (2009).

External links

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References

  • Kropinski, A.M., Mazzocco, A., Waddell, T.E., Lingohr, E. & Johnson, R.P. (2009). Enumeration of bacteriophages by double agar overlay plaque assay. Methods in Molecular Biology 501:69–76. 10.1007/978-1-60327-164-6_7

How to cite this page

Abedon, S.T. (2026). Phage Terms. https://terms.phage.org  ·  10.5281/zenodo.20173633

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Soft-Agar Overlay — terms.phage.org — phage.org — Stephen T. Abedon — DOI: 10.5281/zenodo.20173633 — Version 2026.11.14