Half Fraser Broth Selective Supplement
E&O Laboratories Ltd Half Fraser Selective Supplement (LS5003) is selective supplement for the primary enrichment of Listeria spp from food and environmental samples when used with Fraser Broth.Fraser Broth is a modification of the USDA-FSIS (United States Department of Agriculture-Food Safety Inspection Service) UVM secondary enrichment broth and is based on the formula described by Fraser and Sperber. It contains ferric ammonium citrate and
lithium chloride. Blackening of the medium is presumptive evidence of the presence of Listeria. Contrary to early indications, cultures which do not blacken cannot be assumed to be Listeria-free. All Fraser Broth enrichment cultures should be subcultured to plating medium. Fraser Broth has proven to be remarkably accurate in
detecting Listeria spp. in food and environmental samples.
All Listeria spp. hydrolyse aesculin to aesculetin. Aesculetin reacts with ferric ions which results in blackening. Another possible advantage to the addition of ferric ammonium citrate is that it has been shown that ferric ions enhance the growth of Listeria monocytogenes. Lithium chloride is included in the medium to inhibit the growth of enterococci which can also hydrolyse aesculin.
Half Fraser Broth is a modification of Fraser Broth which contains half of the concentration of nalidixic acid and acriflavine hydrochloride to aid in the recovery of stressed cells. Half Fraser Broth is used as the primary enrichment broth in the ISO methodology for the
detection of Listeria.

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