PRINCIPLE Bile esculin medium contains esculin and peptone for nutrition and bile to
inhibit Gram-positive bacteria other than Group D streptococci and enterococci. Bile
esculin azide agar uses sodium azide to inhibit Gram-negative bacteria, but we don’t
include the sodium azide due to safety concerns. Since you’ll be using isolated Gram
positive cultures, it’s unnecessary. Ferric citrate is added as a color indicator.
Esculin is a glycoside (a sugar molecule bonded by an acetyl linkage to an
alcohol) composed of glucose and esculetin. These linkages are easily hydrolyzed
under acidic conditions. Many bacteria can hydrolyze esculin, but few can do so in
the presence of bile.