EMB agar is a differential medium used in identification and isolation of Gram-negative enteric rods. EMB agar also inhibits the growth of Gram-positive organisms. The differential basis of this medium involves two indicator dyes, eosin and methylene blue, that distinguish between lactose fermenting and non-lactose fermenting organisms. Lactose fermenters form colonies with dark centers and clear borders while the non-lactose fermenters form completely coloroless colonies.
