BBE contains gentamicin at a concentration which inhibits most facultative anaerobes. This medium also contains bile, which inhibits anaerobic gram-negative rods except the B. fragilis group and other bile resistant Bacteroides and Fusobacteria. Esculin in the medium permits recognition of esculin hydrolysis by organisms that produce a brown to black coloration in the medium around the colonies. Hemin is added as a growth factor and allows testing for catalase production. This medium is prepared, dispensed, and stored under oxygen-free conditions to prevent the formation of oxidized products prior to use.