Enterococci are more resistant to chlorine in water, hence are better indicators of sewage pollution than Escherichia coli. Until 1984, members of the genus Enterococcus were classified as Group D Streptococci. Upon genomic DNA analysis, a seperate genus status was provided to them. (7). Azide Dextrose Broth is recommended by APHA for enumeration of faecal Streptococci by MPN technique. Azide Dextrose Broth was initially formulated by Rothe, Mullmann and Seligmann (2,3) for quantitative determination of Enterococci in water, sewage, foods and other materials suspected of contamination with sewage. When large volumes of water samples are to be examined, double strength medium is used. Turbidity in tubes indicates presence of Enterococci, however, it should be further confirmed by inoculation in Ethyl Violet Azide Broth (M426).
Azide Dextrose Broth is a highly nutritious medium due to the presence of nutrient rich peptone special, beef extract and dextrose. Sodium azide inhibits growth of gram-negative bacteria, allowing Enterococci to grow (1,4,5).Streptococci detected by the above media should be further identified using chemicals (6).
Directions: Suspend 34.7 grams in 1000 ml distilled water for preparing single strength broth or use 69.4 grams in 1000 ml distilled water for double strength broth. Heat, if necessary, to ensure complete solution. Dispense in test tubes and sterilize by autoclaving at 118°C for 15 minutes.
Warning: Sodium azide has a tendency to form explosive metal azides with plumbing materials. It is advisable to use enough water to flush off the disposables.