Ingredient g/L
Proteose Peptone 5.00
Tryptone 5.00
Yeast extract 5.00
Meat extract B# 5.00
Sodium chloride 20.00
Disodium hydrogen phosphate 9.50
Potassium Dihydrogen phosphate 1.35
Aesculin 1.00
Lithium Chloride 3.00
Nalidixic acid 0.010
Acriflavine hydrochloride (Trypaflavine) 0.0125
# Equivalent to Beef Extract
Final pH (at 25°C): 7.2 + 0.2
Direction :
Suspend 27.4 gms. in 500ml. distilled water. Heat if necessary to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to room temperature and add the contents of one vial of Fraser Supplement . Mix well and pour into sterile tubes or plates.
Principle
This medium contains tryptone, yeast extract and beef extract which provide essential nutrients like carbon and nitrogenous compounds including vitamins, amino acids and trace ingredients. Phosphates provide buffering action to the medium while sodium chloride maintains osmotic equilibrium. Nalidixic acid and acriflavine inhibits the growth of gram – negative and gram - positive organisms respectively except Listeria species.
QC Tests
(I) Dehydrated Medium
Colour: Cream to light yellow
Appearance: Homogeneous Free Flowing powder
(II) Rehydrated medium
pH (post autoclaving/heating): 7.2 ± 0.2
Colour (post autoclaving/heating): Yellow coloured solution with bluish tinge
Clarity (post autoclaving/heating): Clear to slightly opalescent
(III)Q.C. Test Microbiological
Cultural characteristics observed after 24-48 hours at 35- 37°C.
MICROORGANISM (ATCC) GROWTH ESCULIN HYDROLYSIS*
Listeria monocytogenes (19118) Luxuriant +
Staphylococcus aureus (25923) Inhibited -
Escherichia coli (25922) Inhibited -
Enterococcus faecalis (29212) Inhibited -
Key: + = blackening of medium
* = subcultured on Listeria selective agar
Use
For selective enrichment of Listeria species as per ISO11290-1:1997 & ISO11133 2:2003
Storage
Dehydrated medium - - below 30°C Prepared medium– Between 2 to 8°C.