What mechanism occurs to change e.coli color to metallic green sheen on EMB agar.answer like a formula please

Question

What mechanism occurs to change e.coli color to metallic green sheen on EMB agar.answer like a formula please

Answer 1

E. coli produces quite a lot of acid, in the presence of acid, Eosin forms an amide bond with Methylene Blue - this gives the green coloration observe for EMB plates with E. Coli growth.

I don't think I am able to draw the equation out, but if you'd like to see the chemical structure of Eosin see here:

http://omlc.ogi.edu/spectra/PhotochemCAD...

and of Methylene Blue see here

http://omlc.ogi.edu/spectra/mb/index.htm...

An amide bond is basically C=O coupled to an N-H group.  So the carboxylic group from Eosin reacts with the N-H group in methylene blue.