Is Escherichia indole positive?
Indole production is often used to differentiate E. coli from other indole-negative enteric bacteria because 96% of E coli are indole positive, whereas many enterobacterial species are negative in the indole reaction.
Does Escherichia coli produce indole?
In E. coli, indole is produced by tryptophanase (TnaA; EC 4.1. 99.1) that can reversibly convert tryptophan into indole, pyruvate, and ammonia (Newton and Snell, 1965) in the tryptophan pathway in E.
Is E. coli positive or negative for indole?
Biochemical Test and Identification of E. coli
|Nitrate Reduction||Positive (+ve)|
What is indole test for E. coli?
The indole test is a qualitative procedure for determining the ability of bacteria to produce indole by deamination of tryptophan. Using Kovacs method, indole combines, in the presence of a tryptophan rich medium, with p-Dimethylaminobenzaldehyde at an acid pH in alcohol to produce a red-violet compound.
Why do we indole test?
Indole tests may be used as an aid in the identification and differentiation of gram-positive and gram-negative organisms. Additional biochemical testing using pure cultures is recommended for complete identification. The tube test is a more sensitive method of detecting indole than the spot test.
What is the positive result for the indole test?
A positive result is shown by the presence of a red or red-violet color in the surface alcohol layer of the broth. A negative result appears yellow. A variable result can also occur, showing an orange color as a result.
Is Enterobacter indole positive?
Bacteria which give negative results for the indole test include: Actinobacillus spp., Aeromonas salmonicida, Alcaligenes sp., most Bacillus sp., Bordetella sp., Enterobacter sp., most Haemophilus sp., most Klebsiella sp., Neisseria sp., Mannheimia haemolytica, Pasteurella ureae, Proteus mirabilis, P.
How does the indole test work?
In the spot test, indole combines, in the filter paper matrix, at an acid pH with p-Dimethylaminocinnamaldehyde (DMACA) to produce a blue to blue-green compound. Indole Spot Reagent has been reported to be useful in detecting indole production by members of the family Enterobacteriaceae and certain anaerobic species.
Why is the indole test important?
This test demonstrate the ability of certain bacteria to decompose the amino acid tryptophane to indole, which accumulates in the medium. Indole production test is important in the identification of Enterobacteria.
How does an indole test work?
To test for the presence of indole, a by-product of tryptophan metabolism, 5 drops of Kovács reagent should be added to the top of the deep. A positive indole test is indicated by the formation of a red color in the reagent layer on top of the agar deep within seconds of adding the reagent.
Who invented indole test?
This was invented by the Hungarian-Swiss Chemist, Ervin Kovats. Indole production is used as, a tests designed to distinguish among members of the family Enterobacteria. For clinical samples follow appropriate techniques for handling specimens as per established guidelines (4,5).