A viral plaque is a visible structure formed within a cell culture

Cell culture

Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...

, such as bacterial cultures within some nutrient medium (e.g. agar

Agar

Agar or agar-agar is a gelatinous substance derived from a polysaccharide that accumulates in the cell walls of agarophyte red algae. Throughout history into modern times, agar has been chiefly used as an ingredient in desserts throughout Asia and also as a solid substrate to contain culture medium...

). The bacteriophage

Bacteriophage

A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...

 virus

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es replicate and spread, thus generating regions of cell destructions known as plaques.

Counting the number of plaques can be used as a method of virus quantification

Virus Quantification

Virus quantification involves counting the number of viruses in a specific volume to determine the virus concentration. It is utilized in both research and development in commercial and academic laboratories as well as production situations where the quantity of virus at various steps is an...

. These plaques can sometimes be detected visually using colony counter

Colony counter

A colony counter is an instrument used to count colonies of bacteria or other microorganisms growing on an agar plate. Early counters were merely lighted surfaces on which the plate was placed, with the colonies marked off with a felt-tipped pen on the outer surface of the plate while the operator...

s, in much the same way as bacterial colonies are counted; however, they are not always visible to the naked eye, and sometimes can only be seen through a microscope

Microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

, or using techniques such as staining or immunofluorescence

Immunofluorescence

Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on biological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows...

. Special computer systems have been designed with the ability to scan samples in batches.

External links

• An image of Bacteriophage plaques in agar