Oxford Agar Base, sometimes referred to as Oxford Listeria Agar Base is used for the selective isolation of Listeria monocytogenes from food. This medium can be modified with the addition of antibiotics.

Principles Peptones and beef heart digest provide nitrogen, carbon, amino acids and vitamins. Agar is the solidifying agent. Sodium chloride maintains the osmotic balance. Ferric ammonium citrate aids in the differentiation of Listeria spp. Since all Listeria spp. hydrolyze esculin, the addition of ferric ions to the medium will detect the reaction. A blackening of the colony and surrounding medium in cultures containing esculin-hydrolyzing bacteria results from the formation of 6,7-dihydroxycoumarin which reacts with the ferric ions. Selectivity is provided by the presence of lithium chloride in the formula. The high salt tolerance of Listeria is used as a means to markedly inhibit growth of enterococci.

Selectivity is increased by adding various antimicrobial agents to the base via the addition of Modified Oxford Antimicrobial Supplement. This item can be found at the link below.

Modified Oxford Antimicrobial Supplement

• Alpha Bio Oxford Listeria Agar Base
• BD Difco Oxford Media Base Technical Data Sheet