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.