A modification of UVM Medium, Fraser Broth is a secondary selective enrichment broth for the isolation of Listeria spp primarily from food and environmental specimens. The medium is made selective by the inclusion of Nalidixic Acid and Acriflavine. Darkening of the broth following incubation, due to the presence of Aesculin and Ferric Ammonium Citrate, is indicative of the presence of Listeria spp. Lithium Chloride is also included to inhibit the growth of enterococci that would otherwise hydrolyse the Aesculin. This medium is generally used in conjunction with Fraser Broth Half-Strength (BM0647).
NB: It should be noted that the lack of darkening of the broth should not be taken as a final negative result and all Fraser Broth enrichment cultures should be sub-cultured onto an appropriate selective agar medium irrespective of colour.