Eosin methylene blue

Eosin methylene blue (EMB, also known as "Levine's formulation") is a selective and differential media used for the identification of Gram-negative bacteria,[1] specifically the Enterobacteriaceae.

[2] Organisms that ferment lactose appear dark/black or green often with "nucleated colonies"—colonies with dark centers.

This culture media is important in medical laboratories by allowing the identification of enteric bacteria microbes in a short period of time.

[4] On EMB if E. coli is grown it will give a distinctive metallic green sheen (due to the metachromatic properties of the dyes, E. coli movement using flagella, and strong acid end-products of fermentation).

[5] This medium has been specifically designed to discourage the growth of Gram-positive bacteria.