Eosin methylene blue agar is a differential medium used for the detection
and isolation of Gram-negative intestinal pathogens. A combination of eosin and
methylene blue is used as an indicator and allows differentiation between
organisms that ferment lactose and those that do not. Saccharose is also included
in the medium because certain members of the Enterobacteria or coliform group
ferment saccharose more readily than they ferment lactose. In addition, methylene
blue acts as an inhibitor to Gram-positive organisms.