Listeria Enrichment Broth Base is an appropriate medium for the selective enrichment of Listeria in the two-step method according to ISO 11290 for the preparation of Fraser or Half Fraser Broth by adding the respective supplements. It is recommended for the detection of Listeria spp. in food products and in samples from the environment. All Listeria species hydrolyse the aesculin to esculetin, which reacts with iron ions producing a blackening of the medium. Another advantage of this medium is that the addition of ammonium iron (III) citrate improves the growth of L. monocytogenes. Lithium chloride included in the medium, along with nalidixic acid and acryflavine from the supplement, inhibit the growth of the accompanying flora, which can hydrolyse the aesculin. The high amount of sodium chloride inhibits the growth of enterococci. Enzymatic digest of casein, enzymatic digest of animal tissues and meat extract provide nitrogen, vitamins, minerals, and amino acids essential for growth. Yeast extract is the source of vitamins, particularly of the B-group. Phosphate salts act as a buffer system.
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