Bactident® Oxidase is used to support the identification of microorganisms on the basis of their cytochrome c oxidase activity. A positive test result normally means that the bacterium can use oxygen for energy production with an electron transfer chain. Among the medically relevant oxidase positive microorganisms are Aeromonas spp., Vibrio spp., Pseudomonas spp., Campylobacter spp. and Brucella spp.. Enterobacteriaceae, however, are mostly oxidase negative.
The cytochrome oxidase, an enzyme which is widespread in nature, oxidizes the reduced cytochrome c and is thereby itself transformed into a reduced and inactive form. Through transfer of the electrons to molecular oxygen, the reduced cytochrome oxidase is transformed back into the active form. In the presence of molecular oxygen the cytochrome oxidase/cytochrome c system can reduce a whole series of organic substances, among them the so-called NaDi reagent (1-naphthol dimethylparaphenylene diamine), leading to the formation of the condensation molecule indophenol blue. Bactident® Oxidase uses this reaction to identify microorganisms.
Bactident® E. coli
Bactident® E. coli is used for the rapid identification of Escherichia coli. It is based on the detection of two enzymes found in most E. coli strains: β-D-glucuronidase and tryptophanase. β-D-glucuronidase activity is a specific marker for E. coli among the Enterobacteriaceae and is present in 94% of the species’s strains; apart from E. coli, the enzyme can only be detected in a few Salmonella and Shigella species. Tryptophanase activity (i.e. the ability to form indole from tryptophan) is present in 99% of all E. coli strains. Detection of both enzymes is a highly reliable indicator for the presence of E. coli.
Bactident® Indole is used to determine the ability of a microorganism to convert tryptophan into indole. Tryptophan is abundant particularly in tryptically digested peptone, setting free pyruvic acid, ammonia and indole. This reaction is performed by the enzyme system tryptophanase. The indole then reacts with 4-dimethylaminobenzaldehyde to form a dark red dye. As tryptophan, too, gives a color reaction with 4-dimethylaminobenzaldehyde, it must be separated from the indole beforehand. This is achieved by selectively extracting indole with butanol.