Nitrate Broth with Durham Tube

Determine nitrate reduction by bacteria using Thermo Scientific™ Remel™ Nitrate Broth with Durham Tube. The ability to reduce nitrate to nitrite can be used to differentiate and identify various bacteria and is characteristic of the family Enterobacteriaceae¹. Nitrate serves as the source of nitrogen for many bacteria and fungi, but it must be broken down to be utilized. In 1962, Daubner reported that all members of the Enterobacteriaceae tested, with the exception of Erwinia species, reduced nitrate in eight hours².

Organisms that possess nitrate reductase can reduce nitrate to nitrite. Certain bacteria convert nitrate to nitrite, ammonia or nitrogen gas. This process is referred to as denitrification. Nonfermenters and other miscellaneous gram-negative bacilli vary in their ability to reduce nitrates, some being capable of further reducing nitrite to nitrogen gas. The end product of reduction depends on the bacterial species³.

• Ready to use: Prepared liquid media.
• Rapid test: Results within 5-10 minutes.
• Easy to interpret: When zinc dust is added, a red color indicates the presence of unreacted nitrate.
• Available in 2 formats: With Durham Tube (R061534 and R061536), without Durham Tube (R061530 and R061532).

This medium contains 0.1% potassium nitrate (KNO₃) that acts as a substrate to determine nitrate breakdown. Enterobacteriaceae spp. typically reduce nitrate to nitrite. The presence of nitrite is determined by the addition of sulfanilic acid which reacts with the nitrite to form a diazonium salt. This salt then couples with N,N-Dimethyl-α-naphthylamine to form a red dye complex.

Certain organisms reduce nitrite to ammonia or nitrogen gas, leaving no nitrite to react with sulfanilic acid and yielding a colorless result. An additional test must then be performed by adding zinc dust to test for the presence of unreacted nitrate. Zinc dust catalyzes the reaction of nitrate to nitrite. A positive test indicates development of red color within 1-2 minutes after addition of Nitrate Reagents A (R21239) and B (R21242) or no color change within 5-10 minutes after addition of zinc dust. A negative test indicates no color development within 1-2 minutes after addition of Nitrate Reagents A and B and red color development within 5-10 minutes after addition of zinc dust. Therefore, the nitrate reduction test is evidenced by either the presence of a catabolic end product or the absence of nitrate in the medium³.

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