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Name: Wan M.
Status: Student
Age: 12
Location: N/A
Country: N/A
Date: 2001

In microbiology, most people like to use "Bacto Agar". Why are they using "Bacto Agar" instead of plain agar which is also much cheaper as listed in the product catalogue? Thank you.

I am not sure but I seem to remember that Bacto Agar is more purified, so that it contains less traces of compounds other than Agar. This is important if you want to produce plates that are selective. This means you leave out certain nutrients, because you want to select for those organisms that can grow without these (they will have to be able to produce the nutrients themselves). You wouldn't be able to do that if the Agar was not sufficiently pure, since trace amounts of the nutrients would be sufficient for other organisms to grow as well. In that case your plates would not be completely selective.

From experience I also know that plates poured with Bacto Agar are more transparent which makes them easier to look through. Microbiologists like to view a plate from the bottom, which decreases the risk of contamination or condense water to smear the plate.

Dr. Trudy Wassenaar

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