Thread by @ScienceManCam

How do we quantify how much #virus is in a sample (titre). We use a plaque assay, which is why he most commonly used method. Below is a graphical version I've made (on @BioRender) of how it is done in the lab.

But how do they work? - a thread
#SciComm #Virology #phdchat
1/n

Here is a photo of a #SARSCoV2 assay, the virus which causes #COVID19 ( Photo: Müller/Charité). The large areas which are clear are known as plaques which are caused by virus killing cells in a monolayer. More plaques = more virus titre

#virology #sciencetwitter

2/n

The technique was originally developed for #Bacteriophages bit was adapted by Dulbecco in 1952 for animal #viruses. Viral stocks are dilutes 10 fold in series and placed onto a monolayer. After incubation a gel is placed on the layer, restricting infection to nearby cells

3/n

As nearby cells are infected, plaques are formed by cells dying. These can be seen under a #microscope and counted to determine Plaque Forming Units per milliliter (see image). This determines our overal virus titre within our sample or stock
#scicomm #sciencetwitter #phdchat
4/n

But why are the plaques clear and the well bright blue?
A stain called crystal violet is issued . Crystal violet binds to DNA and proteins in non-dead cells staining them purple/violet. As the plaques are dead cells a clear area is formed.

#scicomm #virology #PhDChat

5/n

That's basically all there is to it. #PlaqueAssays are very sensitive (and an art form too apparently) @profvrr actually has a wall of polio plaque assays in his laboratory (virology.ws). They're certainly something