Viral plaque assay

Definition

A viral plaque assay is a laboratory technique used to quantify the number of viral particles in a sample by observing the formation of plaques, which are areas of cell lysis caused by viral infection. This method relies on the ability of a virus to infect and kill host cells, resulting in visible clear zones or plaques on a layer of cells in culture. The size and number of plaques provide crucial information about the virus's infectivity and titer.

5 Must Know Facts For Your Next Test

1. Viral plaque assays are often performed using monolayers of susceptible host cells grown in tissue culture plates, where the viruses can infect and kill these cells.
2. Each plaque corresponds to an individual infectious virus particle that has spread from an infected cell to neighboring cells, leading to localized cell death.
3. The results of a viral plaque assay are typically reported as plaque-forming units (PFU) per milliliter, indicating the number of infectious viral particles present in the sample.
4. This technique is essential for studying viral pathogenesis, testing antiviral drugs, and developing vaccines, as it provides quantitative measures of viral infectivity.
5. Different viruses may require specific host cell types and conditions for optimal plaque formation, making the assay adaptable for various viral studies.

Review Questions

• How does a viral plaque assay allow scientists to determine the infectivity of a virus?
  • A viral plaque assay helps scientists measure the infectivity of a virus by quantifying the number of plaques formed in a culture of host cells. Each plaque results from an individual viral particle infecting and lysing surrounding cells, which creates visible zones of cell death. By counting these plaques, researchers can calculate the virus's titer, providing a clear picture of its ability to infect and replicate within host cells.
• Discuss the significance of understanding cytopathic effects in relation to viral plaque assays.
  • Understanding cytopathic effects (CPE) is crucial when interpreting the results of viral plaque assays because CPE reflects how viruses interact with host cells. CPE can indicate how virulent a virus is and how effectively it can spread through tissues. In a plaque assay, the presence and extent of CPE help confirm that plaques result from genuine viral infections rather than other factors. This correlation enhances the reliability of the assay as a tool for assessing viral behavior and treatment responses.
• Evaluate how variations in host cell type might influence the outcomes of a viral plaque assay and implications for studying different viruses.
  • Variations in host cell type can significantly affect the outcomes of a viral plaque assay because different viruses have specific preferences for certain cell lines based on receptor compatibility and cellular environment. For example, some viruses may only form plaques in specific human or animal cell lines due to necessary cellular factors for entry or replication. This can lead to differences in observed titer levels or even failure to detect some viruses if inappropriate host cells are used. Consequently, selecting suitable host cells is critical for accurately assessing viral infectivity and understanding its pathogenesis.

Related terms

titer: The concentration of viral particles in a solution, usually expressed as the number of infectious units per milliliter.

cytopathic effect (CPE): The visible changes or damage in host cells caused by viral infection, which can be detected under a microscope.

viral replication cycle: The series of stages a virus goes through to infect a host cell, replicate its genetic material, and produce new viral particles.