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Plaque assay



An assay used for virus isolation and purification, and to determine viral titers.


The plaque assay is originally a virological assay developed to count and measure infectivity of bacteriophages. Later, it was applied to count mammalian viruses as well. The plaque assay remains to be the most widely used technique for virus isolation and purification, and to determine viral titers. The basis of the technique is to measure the ability of a single infectious virus to form a “plaque” on a confluent monolayer culture of cells. A plaque is formed as a result of infection of one cell by a single virus particle followed by the replication of that virus, and eventually, the death of the cell. The newly replicated virus particles will then infect and kill surrounding cells. The culture will then be stained with a dye, which stains only viable cells but not the dead cells. Hence, the dead cells in the plaque will appear unstained against the colored background.

Nowadays, the plaque assay is applied to detect cells producing antibodies that destroy erythrocytes (by hemolysis). The basis is the clear plaque that indicates the red blood cells have been hemolysed by the antibodies.

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Sf9 Expression Kit that makes Blue Plaques with X-gal

... Expression kit that makes blue plaques when you stain the Plaque Assay with X-gal. Currently I use Invitrogen's Bac-N-Blue system, which is GREAT! But they ...

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by lunette008
Wed Oct 19, 2011 9:52 pm
Forum: Cell Biology
Topic: Sf9 Expression Kit that makes Blue Plaques with X-gal
Replies: 2
Views: 1399

Plaque assay

My lab experiment resulted in no plaques on my plate. What does this mean. My teacher said that it is a negative result but what does that mean??? Also....a question reads " why was it important to use a hard agar with a soft agar overlay instead of vice versa???" Thank you

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by csumicroa
Thu Dec 14, 2006 2:43 am
Forum: Microbiology
Topic: Plaque assay
Replies: 1
Views: 4088

what is wrong with my plaque assay?

... work now. I got the virus and I wanted to titer it. I did three times plaque assay already, but all three times I didnot get the "clear spot" as described in ...

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by jimse
Fri Sep 29, 2006 1:59 pm
Forum: Cell Biology
Topic: what is wrong with my plaque assay?
Replies: 0
Views: 1356

Re: reply

... There are easier solutions, that do not need any microscope: search for plaque assay? counting.

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by canalon
Mon Jul 11, 2005 3:14 pm
Forum: Microbiology
Topic: bacteriophages
Replies: 5
Views: 4408

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