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Description:The two test tubes depicted here contain the differential growth medium known as nitrate broth, a medium used in the biochemical identification of organisms that are capable of reducing nitrate (NO3-) to nitrite (NO2-), or other nitrogenous compounds via the action of the enzyme nitratase, or nitrate reductase. Inside each of these tubes, is a smaller Durham fermentation tube, which had been inverted in order to catch and sequester any gas, as a result of the reduction of nitrate into nitrogen gas (N2). The pink color in the tube at left indicates a positive nitrate reduction test, as well as the production of N2).
The nitrate broth is composed of the reagents pancreatic digest of gelatin and potassium nitrate. ”Nitrate Broth is recommended as an aid in the identification of aerobic and facultative anaerobic Gram-negative microorganisms by means of the nitrate reduction test.”

”Nitrate Broth with Durham Tube is a basal medium containing potassium nitrate. The microorganism under evaluation is inoculated into the medium and after incubation, nitrate reduction may be determined. The inverted Durham tube serves to trap nitrogen gas produced through denitrification. The medium is evaluated for nitrate reduction by the addition of two reagents which detect the presence of a catabolic end product, and by the addition of zinc dust which detects the absence of remaining nitrate in the medium.”

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Content Providers(s):CDC/ Dr. R. Weaver
Creation Date:1971
Photo Credit:
Links:Becton Dickinson and Company (BD) - Nitrate Broth with Durham Tube; BBL™ Nitrate Broth with Durham Tube
Becton Dickinson and Company (BD) – “BBL™ Nitrate Broth with Durham Tube”: QUALITY CONTROL PROCEDURES
Becton Dickinson and Company (BD) - Difco™ & BBL™ Manual, 2nd Edition; from ”Biochemical tests for identification of medical bacteria, 3rd ed.”, by MacFaddin, 2000, Lippincott Williams & Wilkins, Baltimore, Md.
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Copyright Restrictions:None - This image is in the public domain and thus free of any copyright restrictions. As a matter of courtesy we request that the content provider be credited and notified in any public or private usage of this image.