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Dima Klenchin

Richard D'Ari:
You say that growth "usually stops ... when the OD600 reaches around 2". We routinely find a higher final OD600, between 5 and 7, although the growth rate between 2 and 5+ is very slow.

Isn't it a quite shocking that OD600 is used for so many decades by so many biologists in so many "critical protocols" even though it is entirely dependent on particulars of the spectrophotometer design and thus can vary dramatically from lab to lab?

What is 2 for you might be 5 for me and could, in theory, be 25 for someone else.

I frequently suspect that "OD600" is a single biggest source of irreproducibility in microbiology.

Elio replies: You are dead right. I checked it our myself and found that the results varied with the machine.

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