Phage Plaques
Phage Plaques - Related Videos
13:00
Plaque Assay: A Method to Determine Viral Titer as Plaque Forming Units (PFU)
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2023
Source: Tilde Andersson1, Rolf Lood1 1 Department of Clinical Sciences Lund, Division of Infection Medicine, Biomedical Center, Lund University, 221 00 Lund, Sweden Viruses that infect prokaryotic organisms, called bacteriophages or simply phages, were identified in the early 20th century by Twort (1) and d'Hérelle (2) independently. Phages have since been widely recognized for their therapeutic value (3) and their influence on human (4), as well as global, ecosystems (5). Current concerns have...
10:52
Precise Phage Mutagenesis with NgTET-Assisted CRISPR-Cas Systems
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2025
Here, we present a protocol to reduce DNA modifications in bacteriophages using the NgTET enzyme, enabling efficient and scarless CRISPR-Cas mutagenesis. This method facilitates the genetic engineering of phages for applications in biotechnology and phage therapy.
04:30
Phage Purification from Borrelia burgdorferi
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2026
Source: Eggers, C. H. Phage-Mediated Genetic Manipulation of the Lyme Disease Spirochete Borrelia burgdorferi. J. Vis. Exp. (2022).This video demonstrates the isolation of borrelial phage particles from a Borrelia burgdorferi suspension using polyethylene glycol-mediated phase separation. The sample is centrifuged, treated with a salt solution, and a molecular crowding agent to precipitate phages. Chloroform extraction is done to remove debris and concentrate phage particles. The purified phage...
03:17
Measuring Spontaneous Phage Induction in Lysogenic Bacteria Over Time
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2026
Source: Krishnamurthi, R., et al. Understanding the Impact of Temperate Bacteriophages on Their Lysogens Through Transcriptomics. J. Vis. Exp. (2024).This video demonstrates the temporal enumeration of spontaneous phage induction in lysogenic Pseudomonas aeruginosa by quantifying viable bacterial cells (CFUs) and infective phage particles (PFUs) over time. By sampling at defined intervals during growth and analyzing both colony and plaque formation, the method reveals when spontaneous induction...
12:36
A Protocol for Phage Display and Affinity Selection Using Recombinant Protein Baits
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Cited by 3 •
2014
Phage display is a powerful technique to capture proteins or protein moieties that interact with an immobilized molecule of interest. Once a decision of the type of phage cDNA library to create and screen has been made, the protocol described here permits efficient affinity selection leading to identification of interactors.
FAQs
Soft agar helps keep phage movement localized after an infected bacterium releases progeny. This allows newly produced particles to reach nearby susceptible cells and repeat the lytic cycle within the bacterial lawn. Because infections remain spatially concentrated, regions of bacterial destruction become visible and can be examined as separate evidence of phage activity.
Plaque size and clarity provide indirect information about how effectively a phage infects, replicates in, and spreads through its bacterial host. Larger or clearer zones may indicate more extensive destruction under the assay conditions, whereas differences among plaques can reveal variation in growth characteristics or host susceptibility. These features support comparisons between phages or bacterial strains.
Plaque number provides a measurable estimate of infectious phage activity in the tested sample. Each infectious particle can initiate a localized sequence of infection, replication, cell lysis, and further spread, producing a visible zone. Consequently, counting plaques allows investigators to determine infectious titer and compare phage abundance or activity across samples analyzed under the same conditions.
A plaque assay begins by combining phages with susceptible bacteria and soft agar, followed by placing that mixture into a bacterial lawn. After infection and repeated lytic cycles, phage progeny spread to neighboring cells and create visible cleared regions. Investigators then examine the resulting plaques, considering their number, size, and clarity as experimental readouts.
Visible plaques help investigators identify phage activity within a bacterial culture and support phage isolation. Once detected, plaque number and appearance can be examined alongside the response of different bacterial hosts. These observations contribute to host-range analysis, reveal which bacteria are susceptible, and help distinguish phages with different growth characteristics.
Phage plaques connect cellular infection with population-level changes in bacteria. Their formation demonstrates how replication inside individual host cells can produce neighboring cell destruction across a bacterial lawn. In biology research, plaque assays therefore support quantitative study of bacteriophages, investigation of host susceptibility, and development of bacteriophage-based approaches for studying or controlling bacterial populations.