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Dehydrated Culture Media

AZIDE DEXTROSE BROTH (ROTHE)

Code: CM0868

For the detection of enterococci in water

Typical Formula*

gm/litre

Peptone

20.0

Glucose

5.0

Sodium chloride

5.0

Di-potassium hydrogen phosphate

2.7

Potassium dihydrogen phosphate

2.7

Sodium azide

0.2

Final pH 6.8 ± 0.2 @ 25°C

 
* Adjusted as required to meet performance standards 

Direction
Add 35.6g to one litre of distilled water for single strength broth or 71.2g for double strength broth. Heat gently to dissolve. Dispense into final containers and sterilise by autoclaving at 121°C for 15 minutes.

Description
Azide Dextrose Broth (Rothe) is used for the detection of enterococci in water and sewage1.

The presence of enterococci serves as an indicator of faecal contamination. Enterococci are better indicators than Escherichia coli of sewage pollution in chlorinated waters because they have a greater resistance to chlorine.

Mallmann and Seligmann2 recommended Azide Dextrose Broth for the quantitative determination of enterococci in water, sewage, foods and other materials suspected of contamination with sewage.

A blend of peptone and glucose render Azide Dextrose Broth highly nutritious, and sodium chloride maintains osmotic equilibrium. The use of sodium azide as an inhibitor of Gram-negative organisms has been reported by several workers2,3,4, and the concentration selected provides optimum protection for the enterococci while largely suppressing the Gram-negative flora. The phosphate buffer system controls pH.

Technique
Inoculate 10ml of medium with 1ml of the test sample. Inoculate a further three tubes with 0.1ml, 0.01ml and 0.001ml sample respectively. For samples of 10ml or more, use double strength broth. Incubate all tubes at 35°C and examine for turbidity after 24 and 48 hours. For a more detailed description please consult `Standard Methods for the Examination of Water and Wastewater’.
The presence of enterococci in the sample is indicated by turbidity in the broth.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C.

Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw coloured solution

Quality control

Positive control:

Expected results

Enterococcus faecalis ATCC® 29212*

Turbid growth

Negative control:

 
Escherichia coli ATCC® 25922 *No growth
* This organism is available as a Culti-Loop®

Precautions
This product contains less than 1% azide and has low toxicity. However, when handling the powder, wear gloves, mask and eye protection. When washing azide products down sinks, use sufficient water to prevent accumulation of azide in the plumbing.

References
1.
Greenberg A. E. et al (ed). (1998) Standard Methods for the Examination of Water and Wastewater, 20th ed. APHA, Washington, D.C.
2. Mallmann W. L. and Seligmann E. B. (1950) Am. J. Public Health 40. 286.
3. Edwards S. J. (1933) J. Comp. Path. Therap. 46. 211.
4. Hartman G. (1937) Milchw. Forsch. 18. 166.

 
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