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Indole test positive: appearance of pink layer at top (e.g. Escherichia coli) Like many biochemical tests on bacteria, results of an indole test are indicated by a change in color following a reaction with an added reagent. Pure bacterial culture must be grown in sterile tryptophan or peptone broth for 24–48 hours before performing the test.
To test the broth for indole production, Kovac's reagent. Kovac's reagent consist of amyl alcohol and para-dimethylaminobenzaldehyde and concentrated hydrochloric acid . Kovac's reagent is actually used to determine ability of an organism to separate indole from amino acid tryptophan and it is added after incubation.
Tryptone is commonly used in microbiology to produce lysogeny broth (LB) for the growth of E. coli and other microorganisms. [2] It provides a source of amino acids for the growing bacteria .
The spot indole test is used to determine if a microbe can deaminate tryptophan to produce indole. This test is performed by saturating a piece of filter paper with Indole Kovacs Reagent and scraping a portion of microbe onto the paper. A color to a pink-red color indicates a positive result while no color change indicates the lack of ...
Positive for the phenylalanine test and the Harnstoff urea test P. vulgaris can test positive or negative for citrate. All combine for a Biocode ID of 31406, (Biocode ID 31402, 31404, 31407 all resulting in P. vulgaris with asymptomatic results) for use in the Interpretation Guide/Computer Coding and Identification System.
An indole test will differentiate Enterobacter from Escherichia, as Enterobacter are indole negative and Escherichia is positive. [5] Enterobacter are distinguished from Klebsiella because of their differences in motility. [5] Klebsiella are non-motile, Gram-negative bacilli ranging from 1–2 μm in length. [6]
The Ehrlich reagent is similar to a number of other indole tests: The van Urk reagent, which uses 0.125 g of p-DMAB, 0.2 mL of ferric chloride solution (25 mg/mL) in 100 mL of 65% sulfuric acid. [9] [10] [11] This is sometimes referred to as the Hofmann reagent or p-DMAB-TS (Test Solution) and gives slightly different colours with different ...
This type of test is considered a diffusion test. [18] In agar and broth dilution methods, bacteria are placed in multiple small tubes with different concentrations of antibiotics. [14] Whether a bacterium is sensitive or not is determined by visual inspection or automatic optical methods, after a period of incubation. [5]