Plaque assay

Definition

A plaque assay is a method used to quantify the number of viral particles in a sample by measuring the number of clear zones, or plaques, formed in a layer of host cells due to viral infection. This technique connects the process of viral replication to observable effects on host cells, allowing researchers to evaluate viral infectivity and the efficacy of antiviral treatments.

5 Must Know Facts For Your Next Test

1. Plaque assays are crucial for quantifying viruses because they provide a direct measure of infectious virus particles, as opposed to total virus particles which may include non-infectious forms.
2. In a typical plaque assay, a diluted viral sample is added to a monolayer of susceptible host cells, allowing each infectious virus to form a visible plaque through cell lysis.
3. The number of plaques is counted after incubation, and this number is used to calculate the virus titer, usually expressed as plaque-forming units (PFU) per milliliter.
4. Plaque assays can also help distinguish between different strains or types of viruses based on their plaque morphology, which can reveal differences in virulence and cytopathic effects.
5. This technique is widely used not only in basic virology research but also in clinical settings to monitor viral loads in patients and assess the effectiveness of antiviral drugs.

Review Questions

• How does a plaque assay facilitate the understanding of viral life cycles, particularly in assessing the lytic cycle?
  • A plaque assay allows researchers to observe the consequences of the lytic cycle by counting plaques that represent areas of cell lysis caused by viral replication. Each plaque originates from a single infectious virus particle that successfully infected a host cell and led to cell death. By quantifying the plaques formed after infection, scientists can assess the efficiency of viral replication and the potency of different viruses in terms of their ability to cause lysis in host cells.
• Discuss how plaque assays can be used to compare the infectivity between lytic and lysogenic viruses.
  • Plaque assays can effectively illustrate the differences between lytic and lysogenic viruses by showing how many plaques form over time. Lytic viruses will generate numerous plaques quickly as they cause rapid cell death. In contrast, lysogenic viruses may not produce plaques immediately since they integrate into the host genome and do not lyse cells right away. Analyzing plaque formation over time can reveal insights into how these two types of viruses replicate and spread within a population.
• Evaluate how modifications to the standard plaque assay protocol could enhance our understanding of viral release mechanisms.
  • Modifying the standard plaque assay protocol, such as incorporating different host cell types or using inhibitors that block specific stages of viral replication, can provide deeper insights into viral release mechanisms. For example, researchers might use fluorescent markers or reporter genes to visualize when and how viruses are released from infected cells. These adjustments could lead to more comprehensive data about the timing and conditions necessary for viral spread, ultimately helping develop targeted antiviral strategies that interfere with these processes.

Related terms

Virus titer: The concentration of viral particles in a solution, often expressed as the number of infectious units per volume, determined through methods like plaque assays.

Lytic cycle: A replication cycle of certain viruses where the virus invades a host cell, replicates rapidly, and ultimately causes cell lysis, releasing new viral particles.

Cytopathic effect (CPE): The observable changes or damage in host cells caused by viral infection, which can be used to assess viral replication and pathogenesis.