Indole Test Definition
- It is a qualitative test that tests the conversion of tryptophan into indole.
- The test is performed as a part of the IMViC test that is used to differentiate the members of the Enterobacteriaceae family.
- It is important in the identification of different bacteria like Escherichia coli, Proteus, Morganella, etc.
What is the indole test used for?
The indole test is used to test an organism’s ability to utilize tryptophan and produce indole. The test is used to differentiate members of the Enterobacteriaceae family as a part of the IMViC test. The test also differentiates Proteus mirabilis from other Proteus species.
What is the purpose of the tryptophan to indole test?
It is a qualitative test that tests the conversion of tryptophan into indole. The test is performed as a part of the IMViC test that is used to differentiate the members of the Enterobacteriaceae family. It is important in the identification of different bacteria like Escherichia coli, Proteus, Morganella, etc.
How to identify weak indole producing organisms by spot test?
a conventional tube method requiring overnight incubation, which identifies weak indole producing organisms. Spot indole test is performed by using one of the three methods mentioned below. Saturate a piece of filter paper with the reagent.
What does positive indole test look like?
positive indole test is indicated by the formation of a pink to red color ("cherry-red ring") in the reagent layer on top of the medium within seconds of adding the reagent (Fig. 1b). If a culture is indole negative, the reagent layer will remain yellow or be slightly cloudy (Fig. 1c).
What does the indole test check for?
The indole test screens for the ability of an organism to degrade the amino acid tryptophan and produce indole. It is used as part of the IMViC procedures, a battery of tests designed to distinguish among members of the family Enterobacteriaceae.
What is indole used for in bacteria?
As an intercellular signal molecule, indole controls diverse aspects of bacterial physiology, such as spore formation, plasmid stability, drug resistance, biofilm formation, and virulence in indole-producing bacteria.
What is indole in microbiology?
The indole test is a biochemical test performed on bacterial species to determine the ability of the organism to convert tryptophan into indole. This division is performed by a chain of a number of different intracellular enzymes, a system generally referred to as "tryptophanase."
Which bacteria is indole positive?
Indole-Positive Bacteria Bacteria that test positive for cleaving indole from tryptophan include: Aeromonas hydrophilia, Aeromonas punctata, Bacillus alvei, most Citrobacter spp., Edwardsiella spp., Escherichia coli, Flavobacterium spp., Haemophilus influenzae, most Proteus spp.
What is the significance of indole quizlet?
what is the purpose of the indole test? -the purpose of this test is to determine the ability of microorganisms to degrade the amino acid TRYPTOPHAN.
How does a microorganism produce indole?
Indole is produced by upwards of 85 species of bacteria from the action of the enzyme tryptophanase (TnaA) upon tryptophan. However, even many bacterial species that lack tryptophanase, and therefore do not produce indole, will exhibit changes in behavior in response to the presence of extracellular indole.
Can E. coli be indole negative?
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.
What is the SIM test in microbiology?
Sulfur, Indole, Motility (SIM) Media This is a differential medium. It tests the ability of an organism to do several things: reduce sulfur, produce indole and swim through the agar (be motile). SIM is commonly used to differentiate members of Enterobacteriaceae.
What is the purpose of Kovac's reagent?
Our Kovacs Reagent is used to detect the presence of indole, which is one of the end products from bacterial oxidation of the amino acid, tryptophan. Tryptophan is an amino acid that can be oxidized by some bacteria to form three major end products: indole, pyruvic acid, and ammonia.
Why is indole production 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.
What is the medicinal uses of indole?
Abstract. Indoles constitute extensively explored heterocyclic ring systems with wide range of applications in pathophysiological conditions that is, cancer, microbial and viral infections, inflammation, depression, migraine, emesis, hypertension, etc.
What does indole group do?
As an intercellular signal molecule, indole regulates various aspects of bacterial physiology, including spore formation, plasmid stability, resistance to drugs, biofilm formation, and virulence. A number of indole derivatives have important cellular functions, including neurotransmitters such as serotonin.
What is the Indole test?
Indole test is used to determine the ability of an organism to split amino acid tryptophan to form the compound indole. It is used as part of the IMViC procedures to differentiate members of the family Enterobacteriaceae.
How to remove bacterial colony from agar?
Sweep the colony onto a swab . Add a drop of indole reagent to the colony swab. Add reagent directly to the colony growing on the agar surface.
What is SIM medium?
Three most commonly used agar medium are: Sulfide-indole-motility (SIM) medium: The SIM medium is a multitest agar used to test for indole production while simultaneously determining motility and hydrogen sulfide producing abilities of the isolate.
What is the purpose of MIU?
Motility-indole-urease (MIU) medium: MIU medium is used to test for indole and urease producing characteristics of the organism along with a test for motility. Motility-indole-ornithine (MIO) medium: In addition to testing for indole production, MIO agar is used to test for motility and ornithine decarboxylase.
What is the best way to inoculate tryptophan broth?
Inoculate the tryptophan broth with broth culture or emulsify isolated colony of the test organism in tryptophan broth.
Can you use Mueller-Hinton agar for a spot indole test?
Do not use colonies from Mueller-Hinton agar for test, because tryptophan is destroyed during the acid hydrolysis of casein. Do not use a plate with a nitrate disk, as nitrate can interfere with the spot indole test by inducing false-negative results.
Can you take bacterial inoculum from MacConkey agar?
Note: The bacterial inoculum should not be taken from media that contain dyes such as MacConkey agar and EMB agar because the color of lactose fermenting colonies on this medium can interfere with test interpretation.
What is the Indole test?
Indole test is a biochemical test conducted on bacterial species to detect their ability to produce indole from tryptophan in the presence of a group of enzymes called ‘tryptophanase’. It is a qualitative test that tests the conversion of tryptophan into indole. The test is performed as a part of the IMViC test that is used to differentiate ...
How far away will indole diffuse?
Detectable indole will diffuse to colonies within 5 mm of a 2- to 3-mm colony, giving false-positive results.
Why is indole split?
The ability of an organism to split indole from the amino acid tryptophan is due to the presence of tryptophanase. Tryptophan is an amino acid that undergoes deamination and hydrolysis in the presence of the enzyme tryptophanase. Reductive deamination of tryptophan results in the production of indole via the intermediate molecule indole pyruvic ...
How much xylene is added to Ehrlich's indole reagent?
For Ehrlich’s reagent, 0.5 ml of xylene is added to the tube and inverted to mix well. Further, six drops of Ehrlich’s indole reagent are added down the side of the tube, and the color is observed below the xylene layer.
What is the IMViC test used for?
The test is used to differentiate members of the Enterobacteriaceae family as a part of the IMViC test.
What is Kovac's reagent used for?
For the tube method, Kovac’s reagent is used for aerobic organisms, and Ehrlich’s reagent is used for anaerobes and weak indole producers.
Which reagent is used for spot testing of anaerobic microorganisms?
Only the cinnamaldehyde reagent can be used for spot testing of anaerobic microorganisms. It is a more sensitive reagent, but it is less stable.
What is the principle of the Indole test?
Principle of Indole Test. In the indole test, the growth of bacteria is induced in a tryptone rich medium. Some bacteria possess an intracellular enzyme tryptophase that results in deamination of tryptophan into three end products, namely indole, pyruvic acid and ammonium. The hydrolysis of tryptophan occurs by the removal of the amine (NH 2) ...
How long does it take for an indole test to detect a microorganism?
Conventional indole test is a slow method that requires an incubation period of 24 hours to detect the microorganisms producing indole.
What is the Spot Indole method?
Spot indole method makes the use of p-Dimethylaminocinnamaldehyde reagent that couples with indole to produce a blue-coloured complex. In a conventional method, Kovacs reagent or 4 (p)-dimethylaminobenzaldehyde couples with indole to develop a red-coloured compound or rosindole.
What reagent is used to classify enterobacteriaceae?
It uses Kovacs reagent to classify the members of Enterobacteriaceae. Conversely, the indole test requires Ehrlich’s reagent to distinguish the non-fermentative and anaerobic bacteria. Indole positive bacteria hold an intracellular enzyme ( tryptophanase ), which degrades the tryptophan amino acid into indole, whereas indole negative bacteria lack ...
What is the IMViC test?
It is a part of a biochemical method popularly known as the IMViC test, in which ‘ I ’ stands for the indole test. Indole is one of the end products forming after the deamination or hydrolysis of tryptophan, caused by an enzyme “Tryptophanase”. Indole test generally includes two methods, namely spot indole test and conventional indole test.
How to add little bacterial inoculum?
Add little bacterial inoculum via wooden applicator from any non-selective medium rich in tryptophan like Blood agar media.
Why should inoculum be taken from an isolated colony?
Inoculum should be taken from an isolated colony to prevent the diffusion of indole.
What is the purpose of the indole test?
As far back as 1889, the indole test was used as a means to distinguish between Escherichia coli andEnterobacter aerogenes (4) . The numerous variations of the indole test alone and in combination with other biochemical tests attest to the central role this test has played in the characterization of coliforms (gram-negative nonsporulating bacilli that ferment lactose, producing acid and gas) (5). The indole test is still used as a classic test to distinguish indole-positive E. coli from indole-negativeEnterobacter and Klebsiella. (8)
What is an indole test?
The indole test screens for the ability of an organism to degrade the amino acid tryptophan and produce indole. It is used as part of the IMViC procedures, a battery of tests designed to distinguish among members of the family Enterobacteriaceae.
How long to incubate sheep blood agar?
Inoculate the bacterium to be tested on an agar medium that contains tryptophan. Trypticase soy agar or sheep blood agar can be used. Incubate for 18 to 24 hours at the appropriate temperature to allow for growth.
Is Ehrlich's reagent the same as Kovács reagent?
Ehrlich's reagent, an alternative to Kovács reagent, also contains DMAB, which reacts with indole to produce a red product. The Ehrlich formulation is more sensitive but contains additional toxic or flammable solvents; it is recommended when testing bacterial groups that produce little indole such as nonfermentative bacilli or anaerobes. Kovács reagent is apparently more stable and the absence of the additional organic extraction (required with Ehrlich's) makes Kovács formulation more suitable for undergraduate laboratories.
What enzyme is used to detect indole?
IND : Indole Test-production of indole from tryptophan by the enzyme tryptophanase . Reagent- Indole is detected by addition of Kovac’s reagent.
What is the test to confirm a culture is an Enterobacteriaceae?
Confirm the culture is of an Enterobacteriaceae. To test this, a quick oxidase test for cytochrome c oxidase may be performed.
What is the ODC?
ODC: decarboxylation of the amino acid ornithine by ornithine decarboxylase
How to get the API reading scale?
Get the API Reading Scale (color chart) by marking each test as positive or negative on the lid of the tray. The wells are marked off into triplets by black triangles, for which scores are allocated.
What is API testing?
API identification products are test kits for identification of Gram positive and Gram negative bacteria and yeast.
What is bacterial suspension?
A bacterial suspension is used to rehydrate each of the wells and the strips are incubated. During incubation, metabolism produces color changes that are either spontaneous or revealed by the addition of reagents. All positive and negative test results are compiled to obtain a profile number, which is then compared with profile numbers in a commercial codebook (or online) to determine the identification of the bacterial species.
What compartments do you put sterile oil in?
Add sterile oil into the ADH, LDC, ODC, H2S and URE compartments.
Principle
Quality Control
- Do not use benzaldehyde reagents (including Ehrlich’s and Kova´cs’) if color is not pale yellow.
- Perform QC on each new lot of reagent prior to using them. QC in-house-prepared reagents weekly, as they can deteriorate, especially if not stored at 4°C. Discard if reactions become weak.
- Organisms
Procedure
- Two methods are in use; 1. a rapid or spot indole testin which indole is detected directly from a colony growing on a medium rich in tryptophan. 2. a conventional tube method requiring overnight incubation, which identifies weak indole producing organisms.
Result
- The development of a brown-red to purple-red color (benzaldehyde reagents) or blue color (cinnamaldehyde reagent) within 20 seconds indicates the presence of indole.
- A negative test is colorless or slightly yellow.
Uses
- Spot indole tests along with gram stain results and colony characteristics can assist in the rapid identification of isolates. For example; a flat, dry lactose fermenting (pink) colony on MacConkey...
- Indole test can also aid in species differentiation.
Limitations
- Growth medium must contain an adequate amount of tryptophan. Do not use colonies from Mueller-Hinton agarfor this test, because tryptophan is destroyed during the acid hydrolysis of casein.
- Do not use a plate with a nitrate disk, as nitrate can interfere with the spot indole test by inducing false-negative results.
- Growth medium must contain an adequate amount of tryptophan. Do not use colonies from Mueller-Hinton agarfor this test, because tryptophan is destroyed during the acid hydrolysis of casein.
- Do not use a plate with a nitrate disk, as nitrate can interfere with the spot indole test by inducing false-negative results.
- Only the cinnamaldehyde reagent can be used for spot testing of anaerobic microorganisms. It is the more sensitive reagent, but it is less stable.
- If the rapid indole test is negative, perform a tube test as the isolate could be positive in the more sensitive tube test.
