For phage infected bacteria after plating, when should the "colony" term be used and when "plaque"? I do not know the exact difference.
If you plate out bacteria for counting the number of the alive cells, then they will form colonies.
When you want to count the number of phages or phage infected bacterial cells among all the cells in your sample, then first you plate so many cells that they will form a continuous layer on the agar surface. After overlaying that bacterial mat with virus containing sample (low melting point agar containing phage or phage infected bacteria, etc...), in the original bacterial layer you will see spots where the cells (which used to be there already) are lysed due to the phages. These are the plaques.
Simple Difference:
Colony refers to a cluster of particular bacteria developed in a medium.
Plaque refers to a clear zone, produced by a Phage which is formed by lysis of the bacterial cells in the medium.
Only one addition - sometimes phage plaques are being called "negative colonies", like "anti-colony":)
Amost opposite. In colony you see the growth of cells in circular colony form. In viral plaque assay you destroy the cells within the plaque.
Colony is a visible growth of organism in solid or semisolid medium result form single cell whereas Plaque is clear area formed by lysis of cell or inhibition of growth by agent such as virus(bacteriophage) in cell culture medium.
Colony is viable whereas plaque are dead cell.
Just to add what Dr. ASOK MUKHOPADHYAY said, plaques can be clear or turbid depending on the type of virus. Lysogenic virus will give Turbid plaques whereas Lytic bacteria will give a clear plaque.
A colony is a visible cluster of bacterial growth and a plaque is the lysis of the bacterial colony by an infecting virus which appears transparent
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