The DOI matches its Crossref record; 31 of the 31 references it cites were found in a registry or an index.
A Rapid and Specific Method for the Detection of Indole in Complex Biological Samples
Open accessAbstract
Indole, a bacterial product of tryptophan degradation, has a variety of important applications in the pharmaceutical industry and is a biomarker in biological and clinical specimens. Yet, specific assays to quantitate indole are complex and require expensive equipment and a high level of training. Thus, indole in biological samples is often estimated using the simple and rapid Kovács assay, which nonspecifically detects a variety of commonly occurring indole analogs. We demonstrate here a sensitive, specific, and rapid method for measuring indole in complex biological samples using a specific reaction between unsubstituted indole and hydroxylamine. We compared the hydroxylamine-based indole assay (HIA) to the Kovács assay and confirmed that the two assays are capable of detecting microgram amounts of indole. However, the HIA is specific to indole and does not detect other naturally occurring indole analogs. We further demonstrated the utility of the HIA in measuring indole levels in clinically relevant biological materials, such as fecal samples and bacterial cultures. Mean and median fecal indole concentrations from 53 healthy adults were 2.59 mM and 2.73 mM, respectively, but varied widely (0.30 mM to 6.64 mM) among individuals. We also determined that enterotoxigenic Escherichia coli strain H10407 produces 3.3 ± 0.22 mM indole during a 24-h period in the presence of 5 mM tryptophan. The sensitive and specific HIA should be of value in a variety of settings, such as the evaluation of various clinical samples and the study of indole-producing bacterial species in the gut microbiota.
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“In human feces, indole is detectable at micromolar concentrations (Darkoh et al., 2015)”
From The Microbiota-Gut-Brain Axis (2019) · cites this paper as Darkoh et al., 2015
Citations
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“also reported a colorimetric method that uses hydroxylamine and can discriminate indole from structurally related compounds (Darkoh et al., 2015).”
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“The ability of the strain to produce indole during cultivation was determined using an indole assay [25].”
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“The hydroxylamine-based indole assay (HIA) was used for the determination of indole concentration (Darkoh et al. 2015).”
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“Indole is excreted by gut microbiota as a byproduct of tryptophan metabolism and accumulates to millimolar levels in human feces ( Figure 1A ; Li et al., 2021 ; Darkoh et al., 2015 ; Chappell et al., 2016 ).”
InfluentialVineetha, K. K., Archana, P. R., Rao, B. K., Ballal, M., Dutta, B., Vani Lakshmi, R., & Bhat, R. G. (2024) · Rapid Communications in Mass Spectrometry · doi:10.1002/rcm.9923 · Cited by 1
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“[12] In addition, the Kovac’s reagent reacts less well with indole-3-propionic acid, indole-3-pyruvic acid, and indoxyl sulfate [12], which are naturally occurring indole analogues present in biological samples [4].”
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“According to Darkoh (Darkoh et al., 2015), the indole test is performed to identify isolates in producing indole compounds due to the breakdown of tryptophan amino acids by the tryptophanase enzyme.”
MethodMicrobe-derived indole tunes organ-function and links microbe metabolites to biological ageingPreprint
Xing, P. Y., Jayaraman, A., Zhang, G. W., Martin, K. A., Faylon, L. E., Kjelleberg, S. J., Rice, S. A., Wang, Y., Bello, A. T., Holmes, E. C., et al. (2023) · bioRxiv (Cold Spring Harbor Laboratory) · doi:10.1101/2023.01.24.525337 · Cited by 1
“In contrast, indole concentrations in healthy rodents and humans have been reported to be about 80 nmol/g and 2.6 mM, respectively (Darkoh et al, 2015; Dong et al, 2020).”
BackgroundInfluentialBibek, G. C., Zhou, P., Naha, A., Gu, J., & Wu, C. (2023) · bioRxiv (Cold Spring Harbor Laboratory) · doi:10.1101/2023.04.24.538132 · Cited by 1
“Additionally, the indole assay provides a quantitative method for detecting indole levels (47).”
MethodSubstrate availability and dietary fibre regulate metabolism of tryptophan by human gut microbesPreprint
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Metadata
- Authors
- Darkoh, C., Chappell, C., Gonzales, C., & Okhuysen, P.
- Affiliations
- The University of Texas Health Science Center at Houston (US)
- The University of Texas MD Anderson Cancer Center (US)
- Venue
- Applied and Environmental Microbiology
- Publisher
- American Society for Microbiology
- Published
- 2015-12
- Volume
- 81
- Issue
- 23
- Pages
- 8093-8097
- ISSN
- 0099-2240 (ISSN-L)
- 1098-5336
- PMC
- PMC4651089
- OpenAlex
- W2260701616
- Semantic Scholar
- c738683cc725688e7523668357b4d9797097bcfa
- Cited by
- 156
- References
- 31
- Citations by year
- 2026: 21 · 2025: 19 · 2024: 13 · 2023: 27 · 2022: 18 · 2021: 12 · 2020: 17 · 2019: 12 · 2018: 10 · 2017: 4 · 2016: 2
- FWCI
- 4.41
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Applied and Environmental Microbiology (publishedVersion)
- Europe PMC (PubMed Central) (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Funders
- National Institute of Allergy and Infectious Diseases (R01AI116914)
- National Institute of Diabetes and Digestive and Kidney Diseases (DK56338, P30DK056338)
- Topics
- Health Sciences › Medicine › Microbiology (medical) › Bacterial Identification and Susceptibility Testing
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Polyamine Metabolism and Applications
- Physical Sciences › Chemistry › Analytical Chemistry › Analytical Methods in Pharmaceuticals
- Keywords
- tryptophan degradation, enterotoxigenic Escherichia coli, gut microbiota, biomarkers, bacterial metabolites
- MeSH terms
- Bacteriological Techniques, Environmental Microbiology, Feces, Humans, Indoles, Sensitivity and Specificity, Tryptophan, Hydroxylamine, Enterotoxigenic Escherichia coli
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