Listeria Agar Base Oxford ISO
Principles and uses
Listeria Agar Base Oxford is a selective medium for Listeria according to the Oxford formula and it is recommended for the detection of Listeria monocytogenes from clinical samples and food products. It is used for a direct sample inoculation or for confirmation after using Listeria Enrichment Broth Base
All Listeria species hydrolyze the esculin to esculetin, which reacts with the iron ions producing black colonies and a blackening of the medium. Another advantage of this medium is that peptones and maize starch provides a rich nutrient base for growth, and the addition of Ferric ammonium citrate improves the growth of L. monocytogenes. Lithium chloride is an inhibiting agent, together with the other antibiotics from the supplement, which inhibit the growth of gram-negative bacteria and a large part of Gram-positive ones. Cycloheximide inhibits yeasts.
Preparation
Suspend 27,8 grams of the medium in 500 ml of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 ºC for 15 minutes. Cool to 45-50 ºC and aseptically add one vial of Oxford Listeria Selective Supplement . Homogenize gently and dispense into Petri dishes.