Ready-to-reconstitute media bags for Half Fraser Broth contain exactly the correct amount of dehydrated culture media and supplements to prepare 20 L of enrichment broth. The dehydrated culture media contained in each bag has been sterilized via irradiation and needs reconstituting with sterile deionized/RO water.
Half Fraser (Demi-Fraser) Broth (ISO) is a selective medium used for the primary enrichment of Listeria monocytogenes and Listeria spp., as described in ISO 11290-1:2017. Half Fraser (Demi-Fraser) Broth (ISO) was developed as a modification of UVM medium (NCM0012) and is based on the formula as described by Fraser and Sperber. Listeria spp. hydrolyze the esculin to esculetin, which reacts with the ferric ammonium citrate (NCM4009), resulting in a black precipitate and a visible positive reaction.
Lithium chloride suppresses the growth of Enterococci in the medium, as Enterococci can also hydrolyze esculin. Enzymatic digestion of animal tissues, casein, meat extract, and yeast extract provides essential vitamins, minerals, amino acids, nitrogen, and carbon, while sodium chloride maintains the osmotic balance. The selective components acriflavine and nalidixic acid are blended into the base powder and inhibit the growth of Escherichia coli. Ferric ammonium citrate is added to the tempered broth after sterilization.
According to ISO 11290-1:2017, the test portion is inoculated into the primary enrichment medium Half Fraser (Demi-Fraser) Broth (ISO), followed by secondary enrichment in Fraser Broth (ISO), and then sub-cultured onto Harlequin® Listeria Chromogenic Agar according to Ottaviani and Agosti (NCM1004). The medium conforms to the performance and formulation requirements of ISO 11290-1:2017.
