What Is Quantal Assay

Monolayer

Monolayer

Cytopathic Effect Cell Culture

Figure 14.2 Preparation of Primary Cell Culture

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Figure 14.2 Preparation of Primary Cell Culture particular virus and are referred to as the cytopathic effect of the virus (figure 14.3). Sometimes the cytopathic effect is localized to particular sites within infected cells. The most common cyto-pathic effect of this type is termed an inclusion body. It is the site at which the virus is being assembled or viral components are being actively synthesized. The sites in the cell where inclusion bodies localize vary depending on the virus. Thus, the presence of a virus in an unknown sample and some idea of its identity can often be gained by culturing the specimen on cells in tissue culture.

Quantitation

Tissue culture is also used in virology to study the number of virions in a sample. The most commonly used method for detecting and quantifying the amount of virus present in any sample is the plaque assay. A number of other methods can be used for quan-

Adenovirus Pap Cytopathic Effect

Figure 14.3 Cytopathic Effects of Virus Infection on Tissue Culture

(a) Fetal tonsil diploid fibroblasts growing as a monolayer, uninfected. (b) Same cells infected with adenovirus. (c) Same cells infected with herpes simplex virus. Note that the monolayer is totally destroyed.

Figure 14.3 Cytopathic Effects of Virus Infection on Tissue Culture

(a) Fetal tonsil diploid fibroblasts growing as a monolayer, uninfected. (b) Same cells infected with adenovirus. (c) Same cells infected with herpes simplex virus. Note that the monolayer is totally destroyed.

titating the number of virions. These include the counting of virions using an electron microscope, quantal assays, and in the case of some animal viruses, hemagglutination.

Plaque Assay

The plaque assay involves determining the number of viruses in solution by adding a known volume of the solution to actively metabolizing cells in a Petri dish. The infection, lysis, and subsequent infection of surrounding cells leads to a clear zone or plaque surrounded by the uninfected cells (figure 14.4). Each plaque represents one virion, initially infecting one cell, and so the number of virions in the original solution can be readily determined. Plaques are only formed by infective viruses and can be used with any viruses that lyse their host cells, including bacteriophage (see figure 14.4b).

It is possible to prepare large numbers of viruses for future studies by adding some liquid to the plate, scraping the surface of the plate with a glass rod, and harvesting the virions.

Counting of Virions with the Electron Microscope

If reasonably pure preparations of virions are obtainable, their concentration may be readily determined by counting the num-

(a)
Bacteriophage Plaque
Figure 14.4 Viral Plaques (a) Plaques formed by the poliovirus infecting a monolayer of cells that have been stained. (b) Plaques formed by bacteriophage.

ber of virions in a specimen prepared for the electron microscope (figure 14.5). This method often may distinguish between infective and non-infective virions. From their shape and size, it also provides clues as to the identity of the virus.

Quanta! Assays

Quantal assays can often provide an approximate virus concentration. In this assay, several dilutions of the virus preparation are administered to a number of animals, cells, or chick embryos, depending on the host specificity of the virus. The titer of the virus, or the endpoint, is the dilution at which 50% of the inoculated hosts are infected or killed. This titer can be reported as either the ID50, infective dose, or the LD50, lethal dose.

Hemagglutination

Some animal viruses clump or agglutinate red blood cells because they interact with the surfaces of the cells. This phenomenon is called hemagglutination. In this process, a virion attaches to two red blood cells simultaneously and causes clumping (figure 14.6a). Sufficiently high concentrations of virus cause aggregation of red blood cells, which is readily visible (figure 14.6b).

14.2 Methods Used to Study Viruses

Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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Responses

  • sandra
    What is quantal assay?
    4 years ago
  • thomas
    Which virus quantal assay?
    2 years ago
  • ANKE
    What are the method used for quantifying the number of virions in a sample?
    1 year ago

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