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Code: SR0046

Description
Fildes Extract is prepared by the action of the enzyme pepsin on defibrinated horse blood at optimum temperature and pH value, as described by Fildes¹. It is a rich source of growth factors, including haemin and coenzyme, derived from the blood cells from which it is prepared. As some of the growth factors are thermolabile it should not be heated above 55°C.
The extract is supplied in screw-capped bottles. Add to the appropriate medium only after the medium has been sterilised.

Technique
Fildes Extract is recommended for the preparation of many culture media among which are the following examples:
Nagler Medium
Melt 100ml sterile nutrient agar, Blood Agar Base CM0055 is recommended, and cool to approximately 50°C. Add 5ml of Fildes Extract and 20ml serum or plasma. Pour plates and dry. Concentrated Egg Yolk Emulsion SR0047 may be used in 5% concentration.
Fildes Broth (Fildes Peptic Blood Broth)
Add 5ml of Fildes Extract to 100ml of Nutrient Broth No.2 CM0067 or other liquid nutrient media.
Fildes Agar (Fildes Peptic Blood Agar)
Melt 100ml of nutrient agar or Blood Agar Base CM0055, cool to 50°C and add 5ml of Fildes Extract.
Fildes Broth and Agar, which are transparent and have the colour of nutrient broth or agar, give copious growths of Haemophilus influenzae and are admirably suited for the primary isolation of this organism.

References
1. Willis A. T. and Hobbs G. (1959) J. Path. Bact. 77. 511-521.
2. Willis A. T. (1977) Anaerobic Bacteriology 3rd Edn. Butterworths London.