Half Fraser Broth in Bags

Half Fraser broth is a selective enrichment medium designed to help the recovery of Listeria sp. This medium contains peptone, casein, yeast extract, and meat extract, which provide essential nutrients like carbon and nitrogenous compounds, including vitamins, amino acids, and trace ingredients. Phosphates buffer the medium while sodium chloride maintains osmotic equilibrium. Nalidixic acid and acriflavine inhibit the growth of Gram-negative and Gram-positive organisms respectively, except Listeria sp. Listeria sp. hydrolyze esculin to glucose and esculetin. The latter combines with ferric ions of ferric ammonium citrate, resulting in the formation of 6-7-Dihydroxycoumarin, a black-brown complex. Ferric ammonium citrate also enhances the growth of L. monocytogenes. The high salt tolerance (of sodium chloride) of Listeria is used as means to inhibit the growth of Enterococci. Lithium chloride is also used to inhibit Enterococci, which also possess the ability to hydrolyze esculin.

Half Fraser broth is used for the selective pre-enrichment and detection of Listeria sp. in food and environmental specimens.