Impact of Probiotic B. infantis EVC001 Feeding in Premature Infants on the Gut Microbiome, Nosocomially Acquired Antibiotic Resistance, and Enteric Inflammation

2'-Fucosyllactose Promotes Colonization of Akkermansia muciniphila and Prevents Colitis In Vitro and in Mice

Akkermansia muciniphila is a potential candidate for ulcerative colitis prevention. Considering that it utilizes 2'-fucosyllactose (2'FL) for growth, 2'FL can be used to enrich the abundance of A. muciniphila in feces. However, whether the crosswalk between 2'FL and A. muciniphila can promote the intestinal colonization of A. muciniphila remains unclear. In this study, we explored the effect and the underlying mechanism of 2'FL on the colonization of A. muciniphila in vitro and in vivo as well as its alleviating effect on colitis. Our results revealed that 2'FL can serve as a carbon source of A. muciniphila to support the growth and increase cell-surface hydrophobicity and the expression of the genes coding fibronectin-binding autotransporter adhesin to promote the adhesion to Caco2/HT29 methotrexate (MTX) cells but not of galactooligosaccharides (GOS) and glucose. Moreover, 2'FL could increase the host mucin formation to promote the adhesion of A. muciniphila to Caco2/HT29 MTX cells but not of GOS and glucose. Furthermore, 2'FL could significantly increase the colonization of A. muciniphila in the gut to alleviate colitis in mice. Overall, the interplay between A. muciniphila and 2'FL is expected to provide an advantageous ecological niche for A. muciniphila so as to confer further health benefits against colitis.

More than nutrition: Therapeutic potential and mechanism of human milk oligosaccharides against necrotizing enterocolitis

Human milk is the most valuable source of nutrition for infants. The structure and function of human milk oligosaccharides (HMOs), which are key components of human milk, have long been attracting particular research interest. Several recent studies have found HMOs to be efficacious in the prevention and treatment of necrotizing enterocolitis (NEC). Additionally, they could be developed in the future as non-invasive predictive markers for NEC. Based on previous findings and the well-defined functions of HMOs, we summarize potential protective mechanisms of HMOs against neonatal NEC, which include: modulating signal receptor function, promoting intestinal epithelial cell proliferation, reducing apoptosis, restoring intestinal blood perfusion, regulating microbial prosperity, and alleviating intestinal inflammation. HMOs supplementation has been demonstrated to be protective against NEC in both animal studies and clinical observations. This calls for mass production and use of HMOs in infant formula, necessitating more research into the safety of industrially produced HMOs and the appropriate dosage in infant formula.

Strain-level characterization of health-associated bacterial consortia that colonize the human gut during infancy

Background

The human gut microbiome develops rapidly during infancy, a key window of development coinciding with maturation of the adaptive immune system. However, little is known of the microbiome growth dynamics over the first few months of life and whether there are any generalizable patterns across human populations. We performed metagenomic sequencing on stool samples (n=94) from a cohort of infants (n=15) at monthly intervals in the first six months of life, augmenting our dataset with seven published studies for a total of 4,441 metagenomes from 1,162 infants.

Results

Strain-level de novo analysis was used to identify 592 of the most abundant organisms in the infant gut microbiome. Previously unrecognized consortia were identified which exhibited highly correlated abundances across samples and were composed of diverse species spanning multiple genera. Analysis of a cohort of infants with cystic fibrosis identified one such novel consortium of diverse Enterobacterales which was positively correlated with weight gain. While all studies showed an increased community stability during the first year of life, microbial dynamics varied widely in the first few months of life, both by study and by individual.

Conclusion

By augmenting published metagenomic datasets with data from a newly established cohort we were able to identify novel groups of organisms that are correlated with measures of robust human development. We hypothesize that the presence of these groups may impact human health in aggregate in ways that individual species may not in isolation.

Efficacy and Safety of Bifidobacterium longum Supplementation in Infants: A Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Strategies to stabilize and support overall infant health by increasing the number of Bifidobacterium longum in the infant gut are of interest, but few studies have systematically addressed this issue. We aimed to evaluate the efficacy and safety of Bifidobacterium longum use in infants using meta-analysis.

METHODS

We searched PubMed, EMBASE, Cochrane Library of Systematic Reviews, and SinoMed for publications until 27 July 2022. The main outcomes of interest were weight gain, risk of necrotizing enterocolitis (NEC), and adverse events. Two authors independently performed study screening, risk of bias assessment, and data extraction. Outcome data were extracted from each included study and combined using mean difference (MD) or risk ratio (RR) and finally combined using a fixed-effect model or random-effect model.

RESULTS

A total of 4481 relevant studies were identified, of which 15 were found to be eligible for randomized controlled trials and were included in the meta-analysis. The combined extracted data showed that the intervention group containing Bifidobacterium longum had a significantly lower risk of NEC (RR = 0.539, 95% CI: 0.333, 0.874) compared to the control group. There was no statistical difference between the intervention and control groups regarding weight gain (MD = 0.029, 95% CI: -0.032, 0.090), the occurrence of adverse events (RR = 0.986, 95% CI: 0.843, 1.153), and serious adverse events (RR = 0.881, 95% CI: 0.493, 1.573).

CONCLUSIONS

Bifidobacterium longum may significantly reduce the risk of NEC in infants as well as being safe; thus, further research evidence is needed on whether there is a benefit on weight gain.

Bifidobacterium infantis as a probiotic in preterm infants: a systematic review and meta-analysis

BACKGROUND

Bifidobacterium infantis has special abilities to utilise human milk oligosaccharides. Hence we hypothesised that probiotic supplements containing B. infantis may confer greater benefits to preterm infants than probiotic supplements without B. infantis.

METHODS

A systematic review with meta-analysis was conducted according to standard guidelines. We selected RCTs evaluating probiotics compared to placebo or no treatment in preterm and/or low birth weight infants. Probiotic effects on Necrotizing Enterocolitis (NEC), Late Onset Sepsis (LOS) and Mortality were analysed separately for RCTs in which the supplemented probiotic product contained B. infantis and those that did not contain B. infantis.

RESULTS

67 RCTs were included (n = 14,606), of which 16 used probiotics containing B. infantis (Subgroup A) and 51 RCTs did not (Subgroup B) Meta-analysis of all RCTs indicated that probiotics reduced the risk of NEC, LOS, and mortality. The subgroup meta-analysis demonstrated greater reduction in the incidence of NEC in subgroup A than subgroup B [(relative risk in subgroup A: 0.38; 95% CI, 0.27-0.55) versus (0.67; 95% CI, 0.55-0.81) in subgroup B; p value for subgroup difference: 0.01].

CONCLUSIONS

These results provide indirect evidence that probiotic supplements that include B. infantis may be more beneficial for preterm infants. Well-designed RCTs are necessary to confirm these findings.

IMPACT

Evidence is emerging that beneficial effects of probiotics are species and strain specific. This systematic review analyses if B. infantis supplementation provides an advantage to preterm infants. This is the first systematic review evaluating the effects of probiotics containing B. infantis in preterm infants. The results of this systematic review provides indirect evidence that probiotics that include B. infantis may be more beneficial for preterm infants. These results will help in guiding future research and clinical practice for using B. infantis as a probiotic in preterm infants.

Human milk oligosaccharides modify the strength of priority effects in the Bifidobacterium community assembly during infancy

Despite the significant role of the gut microbiota in infant health and development, little is known about the ecological processes determining gut microbial community assembly. According to ecology theory, the timing and order of arrival of microbial species into an ecosystem affect microbial community assembly, a phenomenon termed priority effects. Bifidobacterium species are recognized as highly abundant early colonizers of the infant's gut, partly due to their ability to selectively utilize human milk oligosaccharides (HMOs) from breast milk. However, the role of priority effects in Bifidobacterium community assembly remains unclear. Here, we investigated the Bifidobacterium community assembly in the gut of 25 breastfed Danish infants longitudinally sampled throughout the first 6 months of life. Our results showed that the breastfed infants were often initially, but temporarily, dominated by suboptimal HMO-utilizing Bifidobacterium taxa, such as B. longum subsp. longum, before more efficient HMO-utilizers such as B. longum subsp. infantis, replaced the first colonizer as the dominant Bifidobacterium taxon. Subsequently, we validated this observation using gnotobiotic mice sequentially colonized with B. longum subsp. longum and B. longum subsp. infantis or vice versa, with or without supplementation of HMOs in the drinking water. The results showed that in the absence of HMOs, order of arrival determined dominance. Yet, when mice were supplemented with HMOs the strength of priority effects diminished, and B. longum subsp. infantis dominated regardless of colonization order. Our data demonstrate that the arrival order of Bifidobacterium taxa and the deterministic force of breast milk-derived HMOs, dictate Bifidobacterium community assembly in the infant's gut.

Bifidobacterium infantis supplementation versus placebo in early life to improve immunity in infants exposed to HIV: a protocol for a randomized trial

INTRODUCTION

Infants who are born from mothers with HIV (infants who are HIV exposed but uninfected; iHEU) are at higher risk of morbidity and display multiple immune alterations compared to infants who are HIV-unexposed (iHU). Easily implementable strategies to improve immunity of iHEU, and possibly subsequent clinical health outcomes, are needed. iHEU have altered gut microbiome composition and bifidobacterial depletion, and relative abundance of Bifidobacterium infantis has been associated with immune ontogeny, including humoral and cellular vaccine responses. Therefore, we will assess microbiological and immunological phenotypes and clinical outcomes in a randomized, double-blinded trial of B. infantis Rosell®-33 versus placebo given during the first month of life in South African iHEU.

METHODS

This is a parallel, randomised, controlled trial. Two-hundred breastfed iHEU will be enrolled from the Khayelitsha Site B Midwife Obstetric Unit in Cape Town, South Africa and 1:1 randomised to receive 8 × 109 CFU B. infantis Rosell®-33 daily or placebo for the first 4 weeks of life, starting on day 1-3 of life. Infants will be followed over 36 weeks with extensive collection of meta-data and samples. Primary outcomes include gut microbiome composition and diversity, intestinal inflammation and microbial translocation and cellular vaccine responses. Additional outcomes include biological (e.g. gut metabolome and T cell phenotypes) and clinical (e.g. growth and morbidity) outcome measures.

DISCUSSION

The results of this trial will provide evidence whether B. infantis supplementation during early life could improve health outcomes for iHEU.

ETHICS AND DISSEMINATION

Approval for this study has been obtained from the ethics committees at the University of Cape Town (HREC Ref 697/2022) and Seattle Children's Research Institute (STUDY00003679).

TRIAL REGISTRATION

Pan African Clinical Trials Registry Identifier: PACTR202301748714019.

CLINICAL

TRIALS

gov: NCT05923333.

PROTOCOL VERSION

Version 1.8, dated 18 July 2023.

Milk oligosaccharide-driven persistence of Bifidobacterium pseudocatenulatum modulates local and systemic microbial metabolites upon synbiotic treatment in conventionally colonized mice

BACKGROUND

Bifidobacteria represent an important gut commensal in humans, particularly during initial microbiome assembly in the first year of life. Enrichment of Bifidobacterium is mediated though the utilization of human milk oligosaccharides (HMOs), as several human-adapted species have dedicated genomic loci for transport and metabolism of these glycans. This results in the release of fermentation products into the gut lumen which may offer physiological benefits to the host. Synbiotic pairing of probiotic species with a cognate prebiotic delivers a competitive advantage, as the prebiotic provides a nutrient niche.

METHODS

To determine the fitness advantage and metabolic characteristics of an HMO-catabolizing Bifidobacterium strain in the presence or absence of 2'-fucosyllactose (2'-FL), conventionally colonized mice were gavaged with either Bifidobacterium pseudocatenulatum MP80 (B.p. MP80) (as the probiotic) or saline during the first 3 days of the experiment and received water or water containing 2'-FL (as the prebiotic) throughout the study.

RESULTS

16S rRNA gene sequencing revealed that mice provided only B.p. MP80 were observed to have a similar microbiota composition as control mice throughout the experiment with a consistently low proportion of Bifidobacteriaceae present. Using 1H NMR spectroscopy, similar metabolic profiles of gut luminal contents and serum were observed between the control and B.p. MP80 group. Conversely, synbiotic supplemented mice exhibited dramatic shifts in their community structure across time with an overall increased, yet variable, proportion of Bifidobacteriaceae following oral inoculation. Parsing the synbiotic group into high and moderate bifidobacterial persistence based on the median proportion of Bifidobacteriaceae, significant differences in gut microbial diversity and metabolite profiles were observed. Notably, metabolites associated with the fermentation of 2'-FL by bifidobacteria were significantly greater in mice with a high proportion of Bifidobacteriaceae in the gut suggesting metabolite production scales with population density. Moreover, 1,2-propanediol, a fucose fermentation product, was only observed in the liver and brain of mice harboring high proportions of Bifidobacteriaceae.

CONCLUSIONS

This study reinforces that the colonization of the gut with a commensal microorganism does not guarantee a specific functional output. Video Abstract.

Determinants of microbial colonization in the premature gut

Abnormal microbial colonization in the gut at an early stage of life affects growth, development, and health, resulting in short- and long-term adverse effects. Microbial colonization patterns of preterm infants differ from those of full-term infants in that preterm babies and their mothers have more complicated prenatal and postnatal medical conditions. Maternal complications, antibiotic exposure, delivery mode, feeding type, and the use of probiotics may significantly shape the gut microbiota of preterm infants at an early stage of life; however, these influences subside with age. Although some factors and processes are difficult to intervene in or avoid, understanding the potential factors and determinants will help in developing timely strategies for a healthy gut microbiota in preterm infants. This review discusses potential determinants of gut microbial colonization in preterm infants and their underlying mechanisms.

Microbiota and growth among infants and children in low-income and middle-income settings

PURPOSE OF REVIEW

Adequate nutrition is essential but insufficient for optimal childhood growth and development. Increasingly, it is clear that the gut microbiota modulates childhood growth and may be particularly important in low-income and middle-income countries (LMIC), where growth faltering, undernutrition, environmental contamination and enteric pathogens are more common. We summarize recent evidence demonstrating the role of the gut microbiota in impacting childhood growth and interventions targeting the gut microbiota to impact growth in children in LMIC settings.

RECENT FINDINGS

Recent studies show that maturation of the infant microbiota is linked with the development of the immune system, which is key to host-microbe symbiosis. Infants lacking Bifidobacterium longum subsp. Infantis, which predominates breastfed microbiome, display immune activation while supplementation is linked to increased immune tolerance and among undernourished children, promotes growth. Microbiome-directed complimentary foods (MDCF) containing local ingredients is a novel strategy to promote gut microbiota development, especially among undernourished children and improve growth. Dietary patterns during pregnancy may drive selection of gut microbial species that impact infant health and growth.

SUMMARY

Growth patterns among children in LMIC settings are closely associated with the diversity and maturity of the infant microbiome. Prebiotics, probiotics, and synbiotics targeting microbiota dysbiosis may impact birth outcomes, infant immune development and infections, and childhood growth in LMIC settings.

Therapeutic Potential of Gut Microbiota and Its Metabolite Short-Chain Fatty Acids in Neonatal Necrotizing Enterocolitis

Short chain fatty acids (SCFAs), the principle end-products produced by the anaerobic gut microbial fermentation of complex carbohydrates (CHO) in the colon perform beneficial roles in metabolic health. Butyrate, acetate and propionate are the main SCFA metabolites, which maintain gut homeostasis and host immune responses, enhance gut barrier integrity and reduce gut inflammation via a range of epigenetic modifications in DNA/histone methylation underlying these effects. The infant gut microbiota composition is characterized by higher abundances of SCFA-producing bacteria. A large number of in vitro/vivo studies have demonstrated the therapeutic implications of SCFA-producing bacteria in infant inflammatory diseases, such as obesity and asthma, but the application of gut microbiota and its metabolite SCFAs to necrotizing enterocolitis (NEC), an acute inflammatory necrosis of the distal small intestine/colon affecting premature newborns, is scarce. Indeed, the beneficial health effects attributed to SCFAs and SCFA-producing bacteria in neonatal NEC are still to be understood. Thus, this literature review aims to summarize the available evidence on the therapeutic potential of gut microbiota and its metabolite SCFAs in neonatal NEC using the PubMed/MEDLINE database.

Effects of Perinatal Antibiotic Exposure and Neonatal Gut Microbiota

Antibiotic therapy is one of the most important strategies to treat bacterial infections. The overuse of antibiotics, especially in the perinatal period, is associated with long-lasting negative consequences such as the spread of antibiotic resistance and alterations in the composition and function of the gut microbiota, both of which negatively affect human health. In this review, we summarize recent evidence about the influence of antibiotic treatment on the neonatal gut microbiota and the subsequent negative effects on the health of the infant. We also analyze the possible microbiome-based approaches for the re-establishment of healthy microbiota in neonates.

Maternal-Child Microbiome and Impact on Growth and Neurodevelopment in Infants and Children: A Scoping Review

BACKGROUND

Pathologic changes in the microbiome (dysbiosis) have been implicated in affecting the growth and neurodevelopment of infants and children. There is evidence to suggest that prenatal and postnatal stressors may be a factor in dysbiosis and there is also a growing body of evidence to suggest that interventions may reduce this negative impact. A scoping review was undertaken to identify association between maternal and/or child microbiome with child growth and neurodevelopment. Additionally, intervention studies such as use of nutritional supplementation and its impact on the microbiome, growth and neurodevelopment were reviewed.

METHODS

An exhaustive literature search identified 654 relevant citations. After review of abstracts, 557 were eliminated, and 97 remained for full text review. We identified and reported on 42 articles which met inclusion criteria.

RESULTS

Seven studies examined associations between microbiome and neurodevelopment and 36 studies evaluated anthropometric measurements, most commonly weight, and microbiota relationships. One study evaluated both growth and neurodevelopment and microbiota. Fourteen studies evaluated supplemental nutrients. Preterm, low birth weight (LBW), and very low birth weight (VLBW) infants were most studied. Findings were inconclusive for consistent associations between microbiota and growth and neurodevelopment. Further, there were no consistent conclusive changes with prescribed treatment interventions.

DISCUSSION

There is a need for high-quality longitudinal studies evaluating repeated developmental assessment measures using consistent microbial analysis techniques to inform conclusions regarding the association between microbiome and infant and child growth and neurodevelopment. Additional intervention studies that may mitigate dysbiosis are warranted.

Translating neonatal microbiome science into commercial innovation: metabolism of human milk oligosaccharides as a basis for probiotic efficacy in breast-fed infants

For over a century, physicians have witnessed a common enrichment of bifidobacteria in the feces of breast-fed infants that was readily associated with infant health status. Recent advances in bacterial genomics, metagenomics, and glycomics have helped explain the nature of this unique enrichment and enabled the tailored use of probiotic supplementation to restore missing bifidobacterial functions in at-risk infants. This review documents a 20-year span of discoveries that set the stage for the current use of human milk oligosaccharide-consuming bifidobacteria to beneficially colonize, modulate, and protect the intestines of at-risk, human milk-fed, neonates. This review also presents a model for probiotic applications wherein bifidobacterial functions, in the form of colonization and HMO-related catabolic activity in situ, represent measurable metabolic outcomes by which probiotic efficacy can be scored toward improving infant health.

Journey of the Probiotic Bacteria: Survival of the Fittest

This review aims to bring a more general view of the technological and biological challenges regarding production and use of probiotic bacteria in promoting human health. After a brief description of the current concepts, the challenges for the production at an industrial level are presented from the physiology of the central metabolism to the ability to face the main forms of stress in the industrial process. Once produced, these cells are processed to be commercialized in suspension or dried forms or added to food matrices. At this stage, the maintenance of cell viability and vitality is of paramount for the quality of the product. Powder products requires the development of strategies that ensure the integrity of components and cellular functions that allow complete recovery of cells at the time of consumption. Finally, once consumed, probiotic cells must face a very powerful set of physicochemical mechanisms within the body, which include enzymes, antibacterial molecules and sudden changes in pH. Understanding the action of these agents and the induction of cellular tolerance mechanisms is fundamental for the selection of increasingly efficient strains in order to survive from production to colonization of the intestinal tract and to promote the desired health benefits.

Human Milk Oligosaccharide Utilization in Intestinal Bifidobacteria Is Governed by Global Transcriptional Regulator NagR

Bifidobacterium longum subsp. infantis is a prevalent beneficial bacterium that colonizes the human neonatal gut and is uniquely adapted to efficiently use human milk oligosaccharides (HMOs) as a carbon and energy source. Multiple studies have focused on characterizing the elements of HMO utilization machinery in B. longum subsp. infantis; however, the regulatory mechanisms governing the expression of these catabolic pathways remain poorly understood. A bioinformatic regulon reconstruction approach used in this study implicated NagR, a transcription factor from the ROK family, as a negative global regulator of gene clusters encoding lacto-N-biose/galacto-N-biose (LNB/GNB), lacto-N-tetraose (LNT), and lacto-N-neotetraose (LNnT) utilization pathways in B. longum subsp. infantis. This conjecture was corroborated by transcriptome profiling upon nagR genetic inactivation and experimental assessment of binding of recombinant NagR to predicted DNA operators. The latter approach also implicated N-acetylglucosamine (GlcNAc), a universal intermediate of LNT and LNnT catabolism, and its phosphorylated derivatives as plausible NagR transcriptional effectors. Reconstruction of NagR regulons in various Bifidobacterium lineages revealed multiple potential regulon expansion events, suggesting evolution from a local regulator of GlcNAc catabolism in ancestral bifidobacteria to a global regulator controlling the utilization of mixtures of GlcNAc-containing host glycans in B. longum subsp. infantis and Bifidobacterium bifidum. IMPORTANCE The predominance of bifidobacteria in the gut of breastfed infants is attributed to the ability of these bacteria to metabolize human milk oligosaccharides (HMOs). Thus, individual HMOs such as lacto-N-tetraose (LNT) and lacto-N-neotetraose (LNnT) are considered promising prebiotics that would stimulate the growth of bifidobacteria and confer multiple health benefits to preterm and malnourished children suffering from impaired (stunted) gut microbiota development. However, the rational selection of HMO-based prebiotics is hampered by the incomplete knowledge of regulatory mechanisms governing HMO utilization in target bifidobacteria. This study describes NagR-mediated transcriptional regulation of LNT and LNnT utilization in Bifidobacterium longum subsp. infantis. The elucidated regulatory network appears optimally adapted to simultaneous utilization of multiple HMOs, providing a rationale to add HMO mixtures (rather than individual components) to infant formulas. The study also provides insights into the evolutionary trajectories of complex regulatory networks controlling carbohydrate metabolism in bifidobacteria.

Strain-specific impacts of probiotics are a significant driver of gut microbiome development in very preterm infants

The development of the gut microbiome from birth plays important roles in short- and long-term health, but factors influencing preterm gut microbiome development are poorly understood. In the present study, we use metagenomic sequencing to analyse 1,431 longitudinal stool samples from 123 very preterm infants (<32 weeks' gestation) who did not develop intestinal disease or sepsis over a study period of 10 years. During the study period, one cohort had no probiotic exposure whereas two cohorts were given different probiotic products: Infloran (Bifidobacterium bifidum and Lactobacillus acidophilus) or Labinic (B. bifidum, B. longum subsp. infantis and L. acidophilus). Mothers' own milk, breast milk fortifier, antibiotics and probiotics were significantly associated with the gut microbiome, with probiotics being the most significant factor. Probiotics drove microbiome transition into different preterm gut community types (PGCTs), each enriched in a different Bifidobacterium sp. and significantly associated with increased postnatal age. Functional analyses identified stool metabolites associated with PGCTs and, in preterm-derived organoids, sterile faecal supernatants impacted intestinal, organoid monolayer, gene expression in a PGCT-specific manner. The present study identifies specific influencers of gut microbiome development in very preterm infants, some of which overlap with those impacting term infants. The results highlight the importance of strain-specific differences in probiotic products and their impact on host interactions in the preterm gut.

Milk glycan metabolism by intestinal bifidobacteria: insights from comparative genomics

Bifidobacteria are early colonizers of the human neonatal gut and provide multiple health benefits to the infant, including inhibiting the growth of enteropathogens and modulating the immune system. Certain Bifidobacterium species prevail in the gut of breastfed infants due to the ability of these microorganisms to selectively forage glycans present in human milk, specifically human milk oligosaccharides (HMOs) and N-linked glycans. Therefore, these carbohydrates serve as promising prebiotic dietary supplements to stimulate the growth of bifidobacteria in the guts of children suffering from impaired gut microbiota development. However, the rational formulation of milk glycan-based prebiotics requires a detailed understanding of how bifidobacteria metabolize these carbohydrates. Accumulating biochemical and genomic data suggest that HMO and N-glycan assimilation abilities vary remarkably within the Bifidobacterium genus, both at the species and strain levels. This review focuses on the delineation and genome-based comparative analysis of differences in respective biochemical pathways, transport systems, and associated transcriptional regulatory networks, providing a foundation for genomics-based projection of milk glycan utilization capabilities across a rapidly growing number of sequenced bifidobacterial genomes and metagenomic datasets. This analysis also highlights remaining knowledge gaps and suggests directions for future studies to optimize the formulation of milk-glycan-based prebiotics that target bifidobacteria.

Capturing the antibiotic resistome of preterm infants reveals new benefits of probiotic supplementation

BACKGROUND

Probiotic use in preterm infants can mitigate the impact of antibiotic exposure and reduce rates of certain illnesses; however, the benefit on the gut resistome, the collection of antibiotic resistance genes, requires further investigation. We hypothesized that probiotic supplementation of early preterm infants (born < 32-week gestation) while in hospital reduces the prevalence of antibiotic resistance genes associated with pathogenic bacteria in the gut. We used a targeted capture approach to compare the resistome from stool samples collected at the term corrected age of 40 weeks for two groups of preterm infants (those that routinely received a multi-strain probiotic during hospitalization and those that did not) with samples from full-term infants at 10 days of age to identify if preterm birth or probiotic supplementation impacted the resistome. We also compared the two groups of preterm infants up to 5 months of age to identify persistent antibiotic resistance genes.

RESULTS

At the term corrected age, or 10 days of age for the full-term infants, we found over 80 antibiotic resistance genes in the preterm infants that did not receive probiotics that were not identified in either the full-term or probiotic-supplemented preterm infants. More genes associated with antibiotic inactivation mechanisms were identified in preterm infants unexposed to probiotics at this collection time-point compared to the other infants. We further linked these genes to mobile genetic elements and Enterobacteriaceae, which were also abundant in their gut microbiomes. Various genes associated with aminoglycoside and beta-lactam resistance, commonly found in pathogenic bacteria, were retained for up to 5 months in the preterm infants that did not receive probiotics.

CONCLUSIONS

This pilot survey of preterm infants shows that probiotics administered after preterm birth during hospitalization reduced the diversity and prevented persistence of antibiotic resistance genes in the gut microbiome. The benefits of probiotic use on the microbiome and the resistome should be further explored in larger groups of infants. Due to its high sensitivity and lower sequencing cost, our targeted capture approach can facilitate these surveys to further address the implications of resistance genes persisting into infancy without the need for large-scale metagenomic sequencing. Video Abstract.

Antimicrobial utilization in very-low-birth-weight infants: association with probiotic use

OBJECTIVE

To examine the association between probiotic use and antimicrobial utilization.

STUDY DESIGN

We retrospectively evaluated very-low-birth-weight (VLBW) infants admitted to tertiary neonatal intensive care units in Canada between 2014 and 2019. Our outcome was antimicrobial utilization rate (AUR) defined as number of days of antimicrobial exposure per 1000 patient-days.

RESULT

Of 16,223 eligible infants, 7279 (45%) received probiotics. Probiotic use rate increased from 10% in 2014 to 68% in 2019. The AUR was significantly lower in infants who received probiotics vs those who did not (107 vs 129 per 1000 patient-days, aRR = 0.89, 95% CI [0.81, 0.98]). Among 13,305 infants without culture-proven sepsis or necrotizing enterocolitis ≥Stage 2, 5931 (45%) received probiotics. Median AUR was significantly lower in the probiotic vs the no-probiotic group (78 vs 97 per 1000 patient-days, aRR = 0.85, 95% CI [0.74, 0.97]).

CONCLUSION

Probiotic use was associated with a significant reduction in AUR among VLBW infants.

Bifidobacteriumlongum subsp. infantis EVC001 Administration Is Associated with a Significant Reduction in the Incidence of Necrotizing Enterocolitis in Very Low Birth Weight Infants

OBJECTIVE

To assess the effects of Bifidobacteriumlongum subsp. infantis EVC001 (Binfantis EVC001) administration on the incidence of necrotizing enterocolitis (NEC) in preterm infants in a single level IV neonatal intensive care unit (NICU).

STUDY DESIGN

Nonconcurrent retrospective analysis of 2 cohorts of very low birth weight (VLBW) infants not exposed and exposed to Binfantis EVC001 probiotic at Oregon Health & Science University from 2014 to 2020. Outcomes included NEC incidence and NEC-associated mortality, including subgroup analysis of extremely low birth weight (ELBW) infants. Log-binomial regression models were used to compare the incidence and risk of NEC-associated outcomes between the unexposed and exposed cohorts.

RESULTS

The cumulative incidence of NEC diagnoses decreased from 11.0% (n = 301) in the no EVC001 (unexposed) cohort to 2.7% (n = 182) in the EVC001 (exposed) cohort (P < .01). The EVC001 cohort had a 73% risk reduction of NEC compared with the no EVC001 cohort (adjusted risk ratio, 0.27; 95% CI, 0.094-0.614; P < .01) resulting in an adjusted number needed to treat of 13 (95% CI, 10.0-23.5) for Binfantis EVC001. NEC-associated mortality decreased from 2.7% in the no EVC001 cohort to 0% in the EVC001 cohort (P = .03). There were similar reductions in NEC incidence and risk for ELBW infants (19.2% vs 5.3% [P < .01]; adjusted risk ratio, 0.28; 95% CI, 0.085-0.698 [P = .02]) and mortality (5.6% vs 0%; P < .05) in the 2 cohorts.

CONCLUSIONS

In this observational study of 483 VLBW infants, Binfantis EVC001 administration was associated with significant reductions in the risk of NEC and NEC-related mortality. Binfantis EVC001 supplementation may be considered safe and effective for reducing morbidity and mortality in the NICU.

Bifidobacterium infantis treatment promotes weight gain in Bangladeshi infants with severe acute malnutrition

Disrupted development of the gut microbiota is a contributing cause of childhood malnutrition. Bifidobacterium longum subspecies infantis is a prominent early colonizer of the infant gut that consumes human milk oligosaccharides (HMOs). We found that the absolute abundance of Bifidobacterium infantis is lower in 3- to 24-month-old Bangladeshi infants with severe acute malnutrition (SAM) compared to their healthy age-matched counterparts. A single-blind, placebo-controlled trial (SYNERGIE) was conducted in 2- to 6-month-old Bangladeshi infants with SAM. A commercial U.S. donor-derived B. infantis strain (EVC001) was administered daily with or without the HMO lacto-N-neotetraose for 28 days. This intervention increased fecal B. infantis abundance in infants with SAM, although to levels still 10- to 100-fold lower than in untreated healthy controls. EVC001 treatment promoted weight gain that was associated with reduced intestinal inflammation markers in infants with SAM. We cultured fecal B. infantis strains from Bangladeshi infants and colonized gnotobiotic mice with these cultured strains. The gnotobiotic mice were fed a diet representative of that consumed by 6-month-old Bangladeshi infants, with or without HMO supplementation. One B. infantis strain, Bg_2D9, expressing two gene clusters involved in uptake and utilization of N-glycans and plant-derived polysaccharides, exhibited superior fitness over EVC001. The fitness advantage of Bg_2D9 was confirmed in a gnotobiotic mouse model of mother-to-infant gut microbiota transmission where dams received a pretreatment fecal community from a SAM infant in the SYNERGIE trial. Whether Bg_2D9 is superior to EVC001 for treating malnourished infants who consume a diet with limited breastmilk requires further clinical testing.

First encounters of the microbial kind: perinatal factors direct infant gut microbiome establishment

The human gut microbiome harbors a diverse range of microbes that play a fundamental role in the health and well-being of their host. The early-life microbiome has a major influence on human development and long-term health. Perinatal factors such as maternal nutrition, antibiotic use, gestational age and mode of delivery influence the initial colonization, development, and function of the neonatal gut microbiome. The perturbed early-life gut microbiome predisposes infants to diseases in early and later life. Understanding how perinatal factors guide and shape the composition of the early-life microbiome is essential to improving infant health. The following review provides a synopsis of perinatal factors with the most decisive influences on initial microbial colonization of the infant gut.

Dynamic Associations of Milk Components With the Infant Gut Microbiome and Fecal Metabolites in a Mother-Infant Model by Microbiome, NMR Metabolomic, and Time-Series Clustering Analyses

Background: The gut microbiome and fecal metabolites of breastfed infants changes during lactation, and are influenced by breast milk components. This study aimed to investigate dynamic associations of milk components with the infant gut microbiome and fecal metabolites throughout the lactation period in a mother–infant model.

Methods: One month after delivery, breast milk and subsequent infant feces were collected in a pair for 5 months from a mother and an exclusively breastfed infant. Composition of the fecal microbiome was determined with 16S rRNA sequencing. Low-molecular-weight metabolites, including human milk oligosaccharides (HMOs), and antibacterial proteins were measured in feces and milk using ¹H NMR metabolomics and enzyme-linked immunosorbent assays. The association of milk bioactive components with the infant gut microbiome and fecal metabolites was determined with Python clustering and correlation analyses.

Results: The HMOs in milk did not fluctuate throughout the lactation period. However, they began to disappear in infant feces at the beginning of month 4. Notably, at this time-point, a bifidobacterium species switching (from B. breve to B. longum subsp. infantis) occurred, accompanied by fluctuations in several metabolites including acetate and butyrate in infant feces.

Conclusions: Milk bioactive components, such as HMOs, might play different roles in the exclusively breastfed infants depending on the lactation period.

Bifidobacterium longum Subspecies infantis Strain EVC001 Decreases Neonatal Murine Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a disease mainly of preterm infants with a 30-50% mortality rate and long-term morbidities for survivors. Treatment strategies are limited and have not improved in decades, prompting research into prevention strategies, particularly with probiotics. Recent work with the probiotic B. infantis EVC001 suggests that this organism may generate a more appropriate microbiome for preterm infants who generally have inappropriate gut colonization and inflammation, both risk factors for NEC. Experimental NEC involving Paneth cell disruption in combination with bacterial dysbiosis or formula feeding was induced in P14-16 C57Bl/6 mice with or without gavaged B. infantis. Following completion of the model, serum, small intestinal tissue, the cecum, and colon were harvested to examine inflammatory cytokines, injury, and the microbiome, respectively. EVC001 treatment significantly decreased NEC in a bacterial dysbiosis dependent model, but this decrease was model-dependent. In the NEC model dependent on formula feeding, no difference in injury was observed, but trending to significant differences was observed in serum cytokines. EVC001 also improved wound closure at six and twelve hours compared to the sham control in intestinal epithelial monolayers. These findings suggest that B. infantis EVC001 can prevent experimental NEC through anti-inflammatory and epithelial barrier restoration properties.

Recent Development of Probiotic Bifidobacteria for Treating Human Diseases

Bifidobacterium is a non-spore-forming, Gram-positive, anaerobic probiotic actinobacterium and commonly found in the gut of infants and the uterine region of pregnant mothers. Like all probiotics, Bifidobacteria confer health benefits on the host when administered in adequate amounts, showing multifaceted probiotic effects. Examples include B. bifidum, B. breve, and B. longum, common Bifidobacterium strains employed to prevent and treat gastrointestinal disorders, including intestinal infections and cancers. Herein, we review the latest development in probiotic Bifidobacteria research, including studies on the therapeutic impact of Bifidobacterial species on human health and recent efforts in engineering Bifidobacterium. This review article would provide readers with a wholesome understanding of Bifidobacteria and its potentials to improve human health.

Impact of a multi-strain probiotic administration on peri-rectal colonization with drug-resistant Gram-negative bacteria in preterm neonates

BACKGROUND

Infections caused by drug resistant Gram-negative bacteria (DR-GNB) are a major health concern for hospitalized preterm neonates, globally. The aim of this study was to investigate the effect of a multi-strain probiotic on the incidence of rectal colonization with DR-GNB in preterm neonates.

METHODS

A double-blind, placebo-controlled, randomized clinical trial was conducted including 200 neonates, randomly allocated to a multi-strain probiotic (n = 100) or placebo (n = 100).

RESULTS

Fifteen percent of the neonates showed peri-rectal colonization with DR-GNB on the day of enrolment indicating probable maternal-to-neonate (vertical) bacterial transmission or environmental acquisition at time of delivery, with no difference between groups. Acquisition of further DR-GNB colonization was rapid, with an increase from 15% on the day enrolment to 77% by day 7 and 83% by day 14 of life. By day 7 (corresponding to early gut colonization), neonates in the probiotic group were 57% less likely to have peri-rectal DR-GNB colonization [OR: 0.43 (0.20-0.95); p = 0.04] and by day 14 (corresponding to late gut colonization), neonates in the probiotic group were 93% less likely to have peri-rectal DR-GNB colonization [OR: 0.07 (0.02-0.23); p < 0.001].

CONCLUSION

Hospitalized neonates showed substantial peri-rectal colonization with DR-GNB at enrolment and further rapid acquisition of DR-GNB in the first 2 weeks of life. The use of a multi-strain probiotic was effective in reducing early and late neonatal gut colonization with DR-GNB.

CLINICAL TRIAL REGISTRATION

The trial was registered at the Pan African Clinical Trial Registry (PACTR202011513390736).

The association between early life antibiotic exposure and the gut resistome of young children: a systematic review

Antimicrobial resistance is a growing public health burden, but little is known about the effects of antibiotic exposure on the gut resistome. As childhood (0-5 years) represents a sensitive window of microbiome development and a time of relatively high antibiotic use, the aims of this systematic review were to evaluate the effects of antibiotic exposure on the gut resistome of young children and identify knowledge gaps. We searched PubMed, Scopus, Web of Science, and the Cochrane Central Register of Controlled Trials. A PICO framework was developed to determine eligibility criteria. Our main outcomes were the mean or median difference in overall resistance gene load and resistome alpha diversity by antibiotic exposure groups. Bias assessment was completed using RoB 2 and ROBINS-I with quality of evidence assessed via the GRADE criteria. From 4885 records identified, 14 studies (3 randomized controlled trials and 11 observational studies) were included in the qualitative review. Eight studies that included information on antibiotic exposure and overall resistance gene load reported no or positive associations. Inconsistent associations were identified for the nine studies that assessed resistome alpha diversity. We identified three main groups of studies based on study design, location, participants, antibiotic exposures, and indication for antibiotics. Overall, the quality of evidence for our main outcomes was rated low or very low, mainly due to potential bias from the selective of reporting results and confounding. We found evidence that antibiotic exposure is associated with changes to the overall gut resistance gene load of children and may influence the diversity of antimicrobial resistance genes. Given the overall quality of the studies, more research is needed to assess how antibiotics impact the resistome of other populations. Nonetheless, this evidence indicates that the gut resistome is worthwhile to consider for antibiotic prescribing practices.

Metabolic model of necrotizing enterocolitis in the premature newborn gut resulting from enteric dysbiosis

Necrotizing enterocolitis (NEC) is a leading cause of premature newborn morbidity and mortality. The clinical features of NEC consistently include prematurity, gut dysbiosis and enteral inflammation, yet the pathogenesis remains obscure. Herein we combine metagenomics and targeted metabolomics, with functional in vivo and in vitro assessment, to define a novel molecular mechanism of NEC. One thousand six hundred and forty seven publicly available metagenomics datasets were analyzed (NEC = 245; healthy = 1,402) using artificial intelligence methodologies. Targeted metabolomic profiling was used to quantify the concentration of specified fecal metabolites at NEC onset (n = 8), during recovery (n = 6), and in age matched controls (n = 10). Toxicity assays of discovered metabolites were performed in vivo in mice and in vitro using human intestinal epithelial cells. Metagenomic and targeted metabolomic analyses revealed significant differences in pyruvate fermentation pathways and associated intermediates. Notably, the short chain fatty acid formate was elevated in the stool of NEC patients at disease onset (P = 0.005) dissipated during recovery (P = 0.02) and positively correlated with degree of intestinal injury (r ² = 0.86). In vitro, formate caused enterocyte cytotoxicity in human cells through necroptosis (P < 0.01). In vivo, luminal formate caused significant dose and development dependent NEC-like injury in newborn mice. Enterobacter cloacae and Klebsiella pneumoniae were the most discriminatory taxa related to NEC dysbiosis and increased formate production. Together, these data suggest a novel biochemical mechanism of NEC through the microbial production of formate. Clinical efforts to prevent NEC should focus on reducing the functional consequences of newborn gut dysbiosis associated metabolic pathways.

Nourishing the Human Holobiont to Reduce the Risk of Non-Communicable Diseases: A Cow’s Milk Evidence Map Example

The microbiome revolution brought the realization that diet, health, and safety for humans in reality means diet, health, and safety for the human holobiont/superorganism. Eating healthier means much more than just feeding human cells. Our diet must also nourish the combination of our microbiome and our connected physiological systems (e.g., the microimmunosome). For this reason, there has been an interest in returning to ancestral “complete” unprocessed foods enriched in microbes, including raw milks. To contribute to this inevitable “nourishing the holobiont” trend, we introduce a systematic risk–benefit analysis tool (evidence mapping), which facilitates transdisciplinary state-of-the-science decisions that transcend single scientific disciplines. Our prior paper developed an evidence map (a type of risk–benefit mind map) for raw vs. processed/pasteurized human breast milk. In the present paper, we follow with a comprehensive evidence map and narrative for raw/natural vs. processed/pasteurized cow’s milk. Importantly, the evidence maps incorporate clinical data for both infectious and non-communicable diseases and allow the impact of modern agricultural, food management, and medical and veterinary monitoring outcomes to be captured. Additionally, we focus on the impact of raw milks (as “complete” foods) on the microimmunosome, the microbiome-systems biology unit that significantly determines risk of the world’s number one cause of human death, non-communicable diseases.

The Potential of Probiotics to Eradicate Gut Carriage of Pathogenic or Antimicrobial-Resistant Enterobacterales

Probiotic supplements have been used to decrease the gut carriage of antimicrobial-resistant Enterobacterales through changes in the microbiota and metabolomes, nutrition competition, and the secretion of antimicrobial proteins. Many probiotics have shown Enterobacterales-inhibiting effects ex vivo and in vivo. In livestock, probiotics have been widely used to eradicate colon or environmental antimicrobial-resistant Enterobacterales colonization with promising efficacy for many years by oral supplementation, in ovo use, or as environmental disinfectants. In humans, probiotics have been used as oral supplements for infants to decease potential gut pathogenic Enterobacterales, and probiotic mixtures, especially, have exhibited positive results. In contrast to the beneficial effects in infants, for adults, probiotic supplements might decrease potentially pathogenic Enterobacterales, but they fail to completely eradicate them in the gut. However, there are several ways to improve the effects of probiotics, including the discovery of probiotics with gut-protection ability and antimicrobial effects, the modification of delivery methods, and the discovery of engineered probiotics. The search for multifunctional probiotics and synbiotics could render the eradication of “bad” Enterobacterales in the human gut via probiotic administration achievable in the future.

Gut Microbiota Development: Influence of Diet from Infancy to Toddlerhood

Early life is a critical period as our gut microbiota establishes here and may impact both current and future health. Thus, it is of importance to understand how different factors govern the complex microbial colonization patterns in this period. The gut microbiota changes substantially during infancy and toddlerhood in terms of both taxonomic composition and diversity. This developmental trajectory differs by a variety of factors, including term of birth, mode of birth, intake of antibiotics, presence of furred pets, siblings and family members, host genetics, local environment, geographical location, and maternal and infant/toddler diet. The type of milk feeding and complementary feeding is particularly important in early and late infancy/toddlerhood, respectively. Breastfeeding, due to the supply of human milk oligosaccharide into the gut, promotes the growth of specific human milk oligosaccharide (HMO)-utilizing Bifidobacterium species that dominate the ecosystem as long as the infant is primarily breastfed. These species perform saccharolytic fermentation in the gut and produce metabolites with physiological effects that may contribute to protection against infectious and immune-related diseases. Formula feeding, due to its lack of HMOs and higher protein content, give rise to a more diverse gut microbiota that contains more opportunistic pathogens and results in a more proteolytic metabolism in the gut. Complementary feeding, due to the introduction of dietary fibers and new protein sources, induces a shift in the gut microbiota and metabolism away from the milk-adapted and toward a more mature and diverse adult-like community with increased abundances of short chain fatty acid-producing bacterial taxa. While the physiological implication of these complementary diet-induced changes remains to be established, a few recent studies indicate that an inadequately matured gut microbiota may be causally related to poor growth and development. Further studies are required to expand our knowledge on interactions between diet, gut microbiota, and health in the early life setting.

Microbiome First Medicine in Health and Safety

Microbiome First Medicine is a suggested 21st century healthcare paradigm that prioritizes the entire human, the human superorganism, beginning with the microbiome. To date, much of medicine has protected and treated patients as if they were a single species. This has resulted in unintended damage to the microbiome and an epidemic of chronic disorders [e.g., noncommunicable diseases and conditions (NCDs)]. Along with NCDs came loss of colonization resistance, increased susceptibility to infectious diseases, and increasing multimorbidity and polypharmacy over the life course. To move toward sustainable healthcare, the human microbiome needs to be front and center. This paper presents microbiome-human physiology from the view of systems biology regulation. It also details the ongoing NCD epidemic including the role of existing drugs and other factors that damage the human microbiome. Examples are provided for two entryway NCDs, asthma and obesity, regarding their extensive network of comorbid NCDs. Finally, the challenges of ensuring safety for the microbiome are detailed. Under Microbiome-First Medicine and considering the importance of keystone bacteria and critical windows of development, changes in even a few microbiota-prioritized medical decisions could make a significant difference in health across the life course.

Milk and bugs educate infant immune systems

Immune-system maturation starts early in life, but studies investigating immune-system education in human infants remain scarce. In a recent issue of Cell, Henrick et al. study early gut microbiota and immune-system development in two infant cohorts. The authors describe that Bifidobacteria can use milk sugars to produce immunoregulatory compounds that induce immune tolerance and reduce intestinal inflammation.

Bifidobacteria-mediated immune system imprinting early in life

Immune-microbe interactions early in life influence the risk of allergies, asthma, and other inflammatory diseases. Breastfeeding guides healthier immune-microbe relationships by providing nutrients to specialized microbes that in turn benefit the host's immune system. Such bacteria have co-evolved with humans but are now increasingly rare in modern societies. Here we show that a lack of bifidobacteria, and in particular depletion of genes required for human milk oligosaccharide (HMO) utilization from the metagenome, is associated with systemic inflammation and immune dysregulation early in life. In breastfed infants given Bifidobacterium infantis EVC001, which expresses all HMO-utilization genes, intestinal T helper 2 (Th2) and Th17 cytokines were silenced and interferon β (IFNβ) was induced. Fecal water from EVC001-supplemented infants contains abundant indolelactate and B. infantis-derived indole-3-lactic acid (ILA) upregulated immunoregulatory galectin-1 in Th2 and Th17 cells during polarization, providing a functional link between beneficial microbes and immunoregulation during the first months of life.

B. infantis EVC001 Is Well-Tolerated and Improves Human Milk Oligosaccharide Utilization in Preterm Infants in the Neonatal Intensive Care Unit

Not all infants carry specialized gut microbes, meaning they cannot digest human milk oligosaccharides and therefore do not receive complete benefits from human milk. B. infantis EVC001 is equipped to convert the full array of complex oligosaccharides into compounds usable by the infant, making it an ideal candidate to stabilize gut function and improve nutrition in preterm infants. A prospective, open-label study design was used to evaluate the tolerability of B. infantis EVC001 and its effects on the fecal microbiota in preterm infants in a Neonatal Intensive Care Unit. Thirty preterm infants <1,500 g and/or <33 weeks gestation at birth were divided into two matched groups, and control infants were enrolled and discharged prior to enrolling EVC001 infants to prevent cross-colonization of B. infantis: (1) fifteen control infants received no EVC001, and (2) fifteen infants received once-daily feedings of B. infantis EVC001 (8.0 x 10⁹ CFU) in MCT oil. Clinical information regarding medications, growth, nutrition, gastrointestinal events, diagnoses, and procedures was collected throughout admission. Infant stool samples were collected at baseline, Study Days 14 and 28, and 34-, 36-, and 38-weeks of gestation. Taxonomic composition of the fecal microbiota, functional microbiota analysis, B. infantis, and human milk oligosaccharides (HMOs) in the stool were determined or quantified using 16S rRNA gene sequencing, metagenomic sequencing, qPCR, and mass spectrometry, respectively. No adverse events or tolerability issues related to EVC001 were reported. Control infants had no detectable levels of B. infantis. EVC001 infants achieved high levels of B. infantis (mean = 9.7 Log10 CFU/μg fecal DNA) by Study Day 14, correlating with less fecal HMOs (ρ = -0.83, P < 0.0001), indicating better HMO utilization in the gut. In this study, B. infantis EVC001 was shown to be safe, well-tolerated, and efficient in colonizing the preterm infant gut and able to increase the abundance of bifidobacteria capable of metabolizing HMOs, resulting in significantly improved utilization of human milk. Clinical Trial Registration: https://clinicaltrials.gov/ct2/show/NCT03939546, identifier: NCT03939546.