BackgroundNext-generation 16S ribosomal RNA gene sequencing is widely used to determine the relative composition of the mammalian gut microbiomes. However, in the absence of a reference, this does not reveal alterations in absolute abundance of specific operational taxonomic units if microbial loads vary across specimens.ResultsHere we suggest the spiking of exogenous bacteria into crude specimens to quantify ratios of absolute bacterial abundances. We use the 16S rDNA read counts of the spike-in bacteria to adjust the read counts of endogenous bacteria for changes in total microbial loads. Using a series of dilutions of pooled faecal samples from mice containing defined amounts of the spike-in bacteria Salinibacter ruber, Rhizobium radiobacter and Alicyclobacillus acidiphilus, we demonstrate that spike-in-based calibration to microbial loads allows accurate estimation of ratios of absolute endogenous bacteria abundances. Applied to stool specimens of patients undergoing allogeneic stem cell transplantation, we were able to determine changes in both relative and absolute abundances of various phyla, especially the genus Enterococcus, in response to antibiotic treatment and radio-chemotherapeutic conditioning.ConclusionExogenous spike-in bacteria in gut microbiome studies enable estimation of ratios of absolute OTU abundances, providing novel insights into the structure and the dynamics of intestinal microbiomes.Electronic supplementary materialThe online version of this article (doi:10.1186/s40168-016-0175-0) contains supplementary material, which is available to authorized users.
Key Points• Urinary 3-IS levels predict outcome after ASCT and are associated with antibiotics and NOD2/CARD15 variants.Indole, which is produced from L-tryptophan by commensal bacteria expressing tryptophanase, not only is an important intercellular signal in microbial communities, but also modulates mucosal barrier function and expression of pro-and anti-inflammatory genes by intestinal epithelial cells. Here, we hypothesized that decreased urinary excretion of 3-indoxyl sulfate (3-IS), the major conjugate of indole found in humans, may be a marker of gut microbiota disruption and increased risk of developing gastrointestinal (GI) graftversus-host-disease. Using liquid chromatography/tandem mass spectrometry, 3-IS was determined in urine specimens collected weekly within the first 28 days after allogeneic stem cell transplantation (ASCT) in 131 patients. Low 3-IS levels within the first 10 days after ASCT were associated with significantly higher transplant-related mortality (P 5 .017) and worse overall survival (P 5 .05) 1 year after ASCT. Least absolute shrinkage and selection operator regression models trained on lognormalized counts of 763 operational taxonomic units derived from next-generation sequencing of the hypervariable V3 region of the 16S ribosomal RNA gene showed members of the families of Lachnospiraceae and Ruminococcaceae of the class of Clostridia to be associated with high urinary 3-IS levels, whereas members of the class of Bacilli were associated with low 3-IS levels. Risk factors of early suppression of 3-IS levels were the type of GI decontamination (P 5 .01), early onset of antibiotic treatment (P 5 .001), and recipient NOD2/ CARD15 genotype (P 5 .04). In conclusion, our findings underscore the relevance of microbiota-derived indole and metabolites thereof in mucosal integrity and protection from inflammation. (Blood. 2015;126(14):1723-1728) IntroductionAllogeneic stem cell transplantation (ASCT) constitutes a potential curative therapy for various hematologic malignancies, bone marrow failure, and immune deficiency syndromes. However, this treatment is still associated with a high risk of mortality because of infectious complications and acute graft-versus-host disease (GVHD). A significant part of these severe complications originates from the gastrointestinal (GI) tract. 1The introduction of 16S ribosomal RNA (rRNA) sequencing has provided novel insights into the diversity and complexity of the gut ecosystem.2 Loss of a diverse composition of the microbiome has been associated with a variety of diseases including inflammatory bowel and autoimmune diseases. At least in part this may be because of the increasingly recognized role that commensal bacteria play in maintaining immunologic homeostasis and epithelial integrity and in exerting anti-inflammatory effects and intestinal tolerance by inducing regulatory T cells. 3,4 Recent studies have demonstrated an association between intestinal bacterial diversity in both mouse models and humans and outcome of ASCT.5-7 A significantly higher ...
In allogeneic stem cell transplantation (ASCT), systemic broad-spectrum antibiotics are frequently used for treatment of infectious complications, but their effect on microbiota composition is still poorly understood. Here, in a retrospective analysis of 621 patients, who underwent ASCT at the University Medical Center of Regensburg and Memorial Sloan Kettering Cancer Center in New York, we assessed the impact of timing of peri-transplant antibiotic treatment on intestinal microbiota composition as well as transplant-related mortality (TRM) and overall survival. Early exposure to antibiotics was associated with lower urinary 3-indoxyl sulfate levels (p<0.001) and a decrease in fecal abundance of commensal Clostridiales (p=0.03) compared to late antibiotic treatment, which was particularly significant (p=0.005) for Clostridium cluster XIVa in the Regensburg group. Earlier antibiotic treatment prior to ASCT was further associated with a higher TRM (34%, n=79/236) compared to post-ASCT (21% n=62/297, p=0.001) or no antibiotics (7% n=6/88, p<0.001). Timing of antibiotic treatment was the dominant independent risk factor for TRM (HR 2.0, p≤0.001) in multivariate analysis beside increase age (HR 2.15, p=0.004), reduced Karnofsky performance status (HR 1.47, p=0.03) and female donor/ male recipient sex combination (HR 1.56, p=0.02) A competing-risk analysis revealed the independent effect of early initiation of antibiotics on GvHD-related TRM (p=0.004) in contrast to infection-related TRM and relapse (p=ns). The poor outcome associated with early administration of antibiotic therapy that is active against commensal organisms, and specifically the possibly protective Clostridiales calls for the use of Clostridiales-sparing antibiotics and rapid restoration of microbiota diversity after cessation of antibiotic treatment.
Analyzing human as well as animal microbiota composition has gained growing interest because structural components and metabolites of microorganisms fundamentally influence all aspects of host physiology. Originally dominated by culture-dependent methods for exploring these ecosystems, the development of molecular techniques such as high throughput sequencing has dramatically increased our knowledge. Because many studies of the microbiota are based on the bacterial 16S ribosomal RNA (rRNA) gene targets, they can, at least in principle, be compared to determine the role of the microbiome composition for developmental processes, host metabolism, and physiology as well as different diseases. In our review, we will summarize differences and pitfalls in current experimental protocols, including all steps from nucleic acid extraction to bioinformatical analysis which may produce variation that outweighs subtle biological differences. Future developments, such as integration of metabolomic, transcriptomic, and metagenomic data sets and standardization of the procedures, will be discussed.
The composition of human as well as animal microbiota has increasingly gained in interest since metabolites and structural components of endogenous microorganisms fundamentally influence all aspects of host physiology. Since many of the bacteria are still unculturable, molecular techniques such as high-throughput sequencing have dramatically increased our knowledge of microbial communities. The majority of microbiome studies published thus far are based on bacterial 16S ribosomal RNA (rRNA) gene sequencing, so that they can, at least in principle, be compared to determine the role of the microbiome composition for host metabolism and physiology, developmental processes, as well as different diseases. However, differences in DNA preparation and purification, 16S rDNA PCR amplification, sequencing procedures and platforms, as well as bioinformatic analysis and quality control measures may strongly affect the microbiome composition results obtained in different laboratories. To systematically evaluate the comparability of results and identify the most influential methodological factors affecting these differences, identical human stool sample replicates spiked with quantified marker bacteria, and their subsequent DNA sequences were analyzed by nine different centers in an external quality assessment (EQA). While high intra-center reproducibility was observed in repetitive tests, significant inter-center differences of reported microbiota composition were obtained. All steps of the complex analysis workflow significantly influenced microbiome profiles, but the magnitude of variation caused by PCR primers for 16S rDNA amplification was clearly the largest. In order to advance microbiome research to a more standardized and routine medical diagnostic procedure, it is essential to establish uniform standard operating procedures throughout laboratories and to initiate regular proficiency testing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.