Oxford Listeria Agar, with addition of antibiotics, is used for the selective isolation of Listeria monocytogenes from food. This medium is utilized with a Ferric Ammonium Citrate supplement for the rapid detection of L. monocytogenes from food and environmental samples. Columbia Blood Agar Base is a general-purpose growth medium. Esculin is the main energy source. All members of the Listeria spp. hydrolyze Esculin to 6,7-dihydroxycoumarine. This compound reacts with Ferric Ammonium Citrate, resulting in the blackening of the medium. Selectivity for Listeria is achieved through the Lithium Chloride included in the formulation and the addition of sterile antimicrobiotic supplements. L. monocytogenes is typically visible after 24 hours, but continued incubation may allow for the detection of slower growing strains.