PRINCIPLE

Listeria monocytogenes hydrolyzes esculin to form esculetin and dextrose. Esculetin reacts with ammonium ferric citrate and forms a
brown-black complex seen as medium blackening. Lithium chloride inhibits the growth of enterococci which can also hydrolyse
aesculin.

PROCEDURE
Inoculate 10ml of Fraser Broth with 0.1ml of the primary enrichment broth (Half Fraser) which has been incubated for 20 to 24 hours.
Incubate at 35 °C for 26 ± 2 hours, aerobically. Even if darkens or not, tubes should be subcultured on Oxford or PALCAM agar.
See also ISO 11290-1:1996 Microbiology of food and animal feeding stuffs - Horizontal method for the detection and enumeration of
Listeria monocytogenes - Part 1: Detection method, and ISO 11290-2:1998 Microbiology of food and animal feeding stuffs - Horizontal
method for the detection and enumeration of
Listeria monocytogenes - Part 2: Enumeration method.

RESULTS & INTERPRETATION
Medium blackening means esculin hydrolysis and presumptive
Listeria monocytogenes presence. Unchanged yellow color cannot
exclude Listeria and culture should be inoculated on plating media for absence confirmation.

QUALITY CONTROL
Listeria monocytogenes ATCC 7644 - blackening.
Pseudomonas aeruginosa ATCC 27853 - yellow.
COMPOSITION
Peptic digest of animal tissue ………….............………………….. 5.0 g
Yeast extract ...…………………………................…………..……..... 5.0 g
Casein enzymic hydrolysate….................…………....…..........…… 5.0 g
Meat extract ………………......................……………………….…… 5.0 g
Sodium chloride ….…………….................………..............……… 20.0 g
Na
2HPO4 * 2H2O ...............…………..……………….................. .... 12.0 g
KH
2PO4 .……………….………………..….............………...….......  1.35 g
Lithium chloride …........………………….…...................…………..  3.0 g
Esculin …........…………………….................………........................  1.0 g
Distilled water ad 1000 ml, pH 7.2 ± 0.2.

FRASER SUPPLEMENT (for 500ml base medium)
Ferric ammonium citrate .......................................................  500.0 mg
Acriflavine hydrochloride .......................................................   25.0 mg
Nalidixic acid ............................................................................ 20.0 mg

HALF FRASER SUPPLEMENT (for 500ml base medium)
Ferric ammonium citrate ..........................................................  500 mg
Acriflavine hydrochloride .......................................................   12.5 mg
Nalidixic acid .............................................................................10.0 mg

Sterilise by autoclaving at 121°C for 15 minutes. Cool to 50°C, and aseptically add the
corresponding selective supplement (Fraser / Half Fraser).

NOTE
Lithium chloride is harmful. Avoid bodily contact and inhalation of vapours.
DESCRIPTION
Fraser Broth Base with added supplement is recommended, as a primary as well as secondary enrichment medium, for the isolation
and enumeration of
Listeria monocytogenes from food and animal feeds.
Fraser Broth
(c) Costin Stoica
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