Fraser HiCynth™ Broth w/ Supplements

Principle And Interpretation

Listeria species are widely distributed and are isolated from soil, decaying vegetable matter, sewage, water, animal feed, fresh and frozen poultry, meats, raw milk, cheese and asymptomatic human and animal carriers (11). Only Listeria monocytogenes from the genus Listeria; causes infections in humans. L. monocytogenes primarily causes meningitis, encephalitis or septicemia in humans (9,12). In pregnant women, Listeria monocytogenes often causes an influenza like bacteremic illness that, if untreated, may lead to ammionitis and infection of the fetus, resulting in abortion, still birth or premature birth. Contaminated foods are the primary vehicles of transmission (8).

Fraser HiCynth™ Broth w/ Supplements is based on the formulation by Fraser and Sperber (2). It is recommended for selective enrichment of Listeria species from foods. Fraser HiCynth™ Broth w/ Supplements is prepared by replacing animal and vegetable peptones with chemically defined peptones to avoid BSE/TSE risks associated with animal peptones.

This medium contains HiCynth Peptone No.3, HiCynth Peptone No.5 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 Acriflavin inhibits the growth of gram-negative and gram-positive organisms respectively (5,6,7) except Listeria species (5,6,7). Listeria species 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 (1). High salt tolerance due to 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.