I decided to “paint’ three different flowers for my microbial art. The one pictured above is my favourite. It is drawn on Eosin Methylene Blue (EMB), which selects for gram-negative bacteria. Lactose fermenters (or other fermenters that create acidic products) cause the medium to turn red or black, and may even turn the colonies black. Fermenters that produce less acid turn pink or red, and bacteria that don’t ferment look translucent or pink in colour.
In my case, the medium stayed about the same colour. I used Escheria coli for the center of the flower. It turned a light pink colour, but not black like I expected (since it is a strong lactose fermenter). I used Serratia marcescens for the petals of the flower, which were a very light shade of pink/white (non-fermenter). Enterobacter aerogenes created the circle around the outer edge of the plate and was a beautiful shade of darker pink/purple (fermenter). The black/purple dots were Chromobacterium violaceum which I thought would become more lightly coloured since it is a non-fermenter. The plate looks better in person, since it is easier to see the various shades of pink.