PRINCIPLE
Medium contains ferric citrate.
L. monocytogenes hydrolyzes esculin to form esculetin and dextrose. Esculetin reacts with ammonium
ferric citrate and forms a brown-black complex seen as a black halo around colonies. Gram-negative bacteria are completely
inhibited. Other Gram-positive are inhibited or grow poorly.

PROCEDURE
See 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
May also be used for direct inoculation

QUALITY CONTROL
Listeria monocytogenes ATCC 7644 - good growth, brown-black  colonies with black halo;
Enterococcus faecalis ATCC 29212 - inhibited;
Bacillus subtilis ATCC 6633 - inhibited;
Escherichia coli ATCC 25922 - inhibited.
COMPOSITION
Columbia Blood Agar Base ………….............………………….. 39.0 g
Aesculin ..………………....................………………………….…… 1.0 g
Ferric ammonium citrate .....……………................………….…… 0.5 g
Lithium chloride …........…….………………..............…….……... 15.0 g
Distilled water ad 1000 ml, pH 7.2 ± 0.2.

SELECTIVE SUPPLEMENT (for 500ml base medium)
Cycloheximide ..................................................................... 200.0 mg
Colistin sulphate ................................................................... 10.0 mg
Acriflavine  ................................................................................. 2.5 mg
Cefotetan ................................................................................... 1.0mg
Fosfomycin ............................................................................... 5.0 mg

MODIFIED SELECTIVE SUPPLEMENT (OXFORD)
Same formulation except Amphotericin B 5 mg replaces Cycloheximide 200 mg.

Sterilise by autoclaving at 121°C for 15 minutes. Cool to 50°C, and aseptically add the
Selective Supplement.

NOTE
Lithium chloride is harmful. Avoid bodily contact and inhalation of vapours.

Variants of medium replace Columbia Blood Agar Base & yeast extract with:
Peptic digest of animal tissue ..................................................... 23.0 g
Starch ................................................................................................. 1.0 g
Sodium chloride ............................................................................... 5.0 g
DESCRIPTION
Listeria Selective Medium (Oxford Formulation) is based on the formulation described by Curtis et al. and is recommended for the
detection of
Listeria monocytogenes from clinical and food specimens.
Oxford Agar
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