Demi-Fraser Broth Base is used with ferric ammonium citrate for the selective enrichment of Listeria species and is not intended for use in the diagnosis of disease or other conditions in humans. The selective components acriflavine and nalidixic acid are blended into the base powder and the ferric ammonium citrate is added to the tempered broth after sterilization. Demi-Fraser Broth Base, is developed to give improved results for the isolation of Listeria spp. with both traditional and ELISA methods. As with the sister product, Fraser Broth Base, the selective components acriflavine and nalidixic acid are blended into the base powder and the Ferric Ammonium Citrate is added to the tempered broth after autoclaving. This format has been shown to give improved selectivity with pure cultures and food samples.
Furthermore, ELISA results are more stable, resulting in fewer false positive results when the ferric ammonium citrate is omitted from the complete media. Developed as a modification of UVM medium and made according to ISO 11290, Fraser Broth is a secondary enrichment broth for the isolation of Listeria spp. and is similar to Palcam Broth in that it contains esculin to indicate the presence of a potential Listeria isolate. It also contains lithium chloride in an attempt to suppress the growth of Enterococci in the medium (as does Palcam). Listeria spp. hydrolyze the esculin to form esculetin, which reacts with the ferric ammonium citrate in resulting in a black precipitate and a visible positive reaction. However, Enterococci can also perform this reaction so further plating is required onto an isolation medium such as Harlequin® Listeria Chromogenic Agar.
