Really quite amazing if you consider how the medium needs to applied, since it grows (changes) over time.

In addition to working as a scientist, and well before his discovery of antibiotics, Fleming painted. He was a member of the Chelsea Arts Club, where he created amateurish watercolors. Less well known is that he also painted in another medium, living organisms. Fleming painted ballerinas, houses, soldiers, mothers feeding children, stick figures fighting and other scenes using bacteria. He produced these paintings by growing microbes with different natural pigments in the places where he wanted different colors. He would fill a petri dish with agar, a gelatin-like substance, and then use a wire lab tool called a loop to inoculate sections of the plate with different species. The paintings were technically very difficult to make. Fleming had to find microbes with different pigments and then time his inoculations such that the different species all matured at the same time. These works existed only as long as it took one species to grow into the others. When that happened, the lines between, say, a hat and a face were blurred; so too were the lines between art and science.

Via smithsonianmag.com.