Mode of Action
Optimum growth conditions are created for Listeria due to the
high nutrient content and the large buffer capacity. The growth
of accompanying bacteria is largely inhibited by lithium
chloride, nalidixic acid and acriflavine hydrochloride. The
detection of the
β-D-glucosidase activity of Listeria is possible by the addition of
esculin and amonium iron(III) citrate. The glucose esculin is
cleaved by β-D-glucosidase into esculetin and glucose. The
esculetin then forms an olive-green to black complex with the
iron(III) ions. Therefore, during the growth of Listeria in FRASER
broth, usually a blackening of the broth is observed. An
improved enrichment of Listeria in comparison with the standard
method can be attained using the two-step enrichment method
with an initially halved concentration of nalidixic acid and
acriflavine hydrochloride.
Typical Composition (g/l