Azide Dextrose Broth

The presence of enterococci is an indicator for faecal contamination, especially when it occurred a long time ago and the less resistant coliform bacteria, including Escherichia coli, may already be dead when the analysis is carried out.

Beef extract and casein peptone provide nitrogen, vitamins, minerals and amino acids essential for growth. Dextrose is the fermentable carbohydrate providing carbon and energy. Sodium chloride supplies essential electrolytes for transport and osmotic balance. The use of sodium azide to selectively inhibit Gram-negative bacteria first appeared in the studies of Edwards (1938) on the isolation of Streptococcus agalactiae; it was later shown that sodium azide can also be used for the isolation of enterococci from water.

Preparation

Suspend 34.7 grams of the medium in one liter of distilled water (69.4 grams if double concentration is desired). Mix well and dissolve by heating with frequent agitation until boiling point. DO NOT OVERHEAT. Dispense into appropriate containers and sterilize in autoclave at 121 °C for 15 minutes.

Instructions for use

1. Take the inoculum with a sterile loop.
2. Submerge the loop into the medium and shake gently.
3. Incubate inoculated tubes at 35 ± 2 °C and observe after 24-48 hours.
4. Turbidity in tubes indicates presence of enterococci; however, it should be further confirmed in EVA Broth (LC-1230).

• American Public Health Association, American Water Works Association and Water Pollution Control Federation: Standard Methods for the Examination of Water and Wastewater, 20th ed., Washington, 1998.
• EDWARDS, S.J.: The diagnosis of Streptococcus mastitis by cultural methods. J. Comp. Path Therap. 51; 250-263 (1938).
• LITSKY, W., MALLMANN, W.L., a. FIFIELD, C.W.: A new medium for the detection of enterococci in water. - Amer. J. Publ. Hlth., 43; 873-879 (1953).
• Verordnung Trinkwasser und über Wasser für Lebensmittelbetriebe (Trinkwasserverordnung) vom 22. Mai 1986. - Bundesgesetzblatt, Teil I, 760-773 (1986).