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Principle
- Half Fraser Broth Base is a modification of Fraser Broth base formulated by Fraser and Sperber (1988) and is used for the detection of Listeria species in food products. It is composed of peptone, tryptone, yeast extract, meat extract, sodium chloride, sodium phosphate dibasic, potassium phosphate monobasic, esculin, lithium chloride, Nalidixic acid and acriflavin.
- Peptone, tryptone, meat extract, and yeast extract provide carbon, nitrogen sources, and essential growth factors required for the growth of Listeria. The high sodium chloride concentration of the medium inhibits the growth of enterococci.
- Sodium phosphate and potassium phosphate act as buffering agents. The Listeria species has the ability to hydrolyze esculin to esculetin. Lithium chloride inhibits gram-negative bacilli.
- Selectivity is provided by nalidixic acid and acriflavine. Nalidixic acid inhibits gram-negative bacteria and acriflavine inhibits gram-positive bacteria.
- For differentiation, the media is fortified with ferric ammonium citrate (Fraser Selective supplement (RDM-FSS-02), which reacts with esculetin to form a black color complex (6-7 dihydroxycoumarin).
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