Sage Journals: Discover world-class research

Abstract

German

Spanish

French

Mouse colonized with human fecal microbiota is an interesting model concept with pros and cons like any other model system. The concept provides an ecologically relevant context to study food component and drug metabolism, and is an invaluable tool for phenotype transfer studies to prove the role of the gut microbiota in health and disease. The major drawbacks are the difficulties with transferring certain components of the human microbiota to the recipient mice, and immunological abnormalities observed in these mice. There seem to be unexplored opportunities for trying to reduce these limitations, but careful evaluation of pros, cons and possible alternatives is still necessary.

Keywords

animal model comparative medicine gut microbiota humanization immunology organisms and models physiology

Introduction

There is a need for in vivo models able to capture the complexity of the human microbiome in conjunction with a biologically relevant host. For several reasons, mice are among the most popular animal models in biomedical research and they are the primary focus of this review. Mice can, with relative ease, be derived to a germ-free (GF) state characterized by the absence of microorganisms, a valuable concept for microbiome researchers. Despite some overlap, there are profound differences between which microorganisms primarily colonize laboratory mice versus humans, which may make mice with a mouse-specific gut microbiota (GM) less translationally relevant. Humanizing the GM of GF rodents is, therefore, a frequently used tool to enhance translation to humans.

The humanized gut microbiota concept

The concept of humanizing the gut microbiota (GM) of mice can take one of two overall paths: a reductionist or a holistic approach. The reductionist approach comprises mono- and multicolonizations with defined organisms and is based on control of which microorganisms are present in the host. This allows for precise mechanistic studies of function and host effects of specific organisms and their inter-organism synergies and interactions.^1,2,3 The holistic approach involves transferring a complex GM from human patients or healthy donors to germ-free (GF) hosts. Mechanistic insights are more difficult to obtain from studies utilizing the holistic approach, whereas it is useful for hypothesis-generation and for proving the causative role of GM in various conditions by phenotype transfer from donor to recipients.

An alternative to using GF recipients is to diminish the existing GM with broad-spectrum antibiotics, an approach discussed elsewhere.⁴ For the reductionist approaches, GF is the only meaningful solution because it allows for precise control of what organisms are present. Holistic colonization with a complex GM may utilize a host with its resident GM depleted by antibiotics,⁵ as long as it is realized that the colonization success can vary according to the microbial diversity in the host prior to antibiotic depletion.⁶

To the best of the author’s knowledge, there are no published reports regarding animal welfare issues related to the transfer of human GM to animals. However, though not experienced by the author, anecdotally people have experienced transient morbidity or even mortality following oral gavage with human feces to GF mice. It seems logical that an inflammatory reaction can happen in response to the intense load of foreign microorganisms, potentially leading to cytokine storm and death—a risk that is likely to be higher in young and immunological naïve GF animals compared with older and antibiotic-treated animals. The procedure of oral gavage implies a risk in itself, for example, volume-related lung obstruction was observed in GF mouse pups after gavage of infant feces.⁷ Increased monitoring following transplantation with human GM is recommended, and publishing of morbidity and loss of animals related to the procedure is encouraged in order to increase awareness and set directions for possible improvements.

Opportunities

The transfer of single organisms, simplistic communities or complex microbiota from humans to GF animals is a simple procedure usually undertaken by oral gavage of a microbial suspension. Once the human GM is established in the new hosts, it remains stable over time when the hosts are housed in isolators or individually ventilated cage systems.^8,9 It is less simple to understand how the physiology of the new host is affected and what that means to the study purpose. Nevertheless, the concept has undoubtedly helped advance our understanding of the capabilities of the microbiome. Table 1 exemplifies recent studies using mice with human GM where model features were deemed relevant to the purpose. There is robust evidence that a human GM in mice responds ecologically and metabolically to dietary changes. The translational value of dietary interventions was demonstrated by identifying modules of bacterial genera allied with intake of a Western diet in mice with human GM and subsequently investigating these genera in a human trial. The preclinically observed changes correctly predicted changes observed in the human study.¹⁰ Within the area of infectious disease, human GM in mice also seem to be relevant, as shown by the ability to protect against Salmonella infection.¹¹ A Clostridium difficile infection model functioned similarly to mice with a mouse GM, but the human GM model was expected to be more ecologically relevant.⁹

Table 1.

Examples of human-to-mouse GM transfer studies and relevant model features.

Research area	Human Donor	Recipient	Model induction	Model features
Obesity	Obese adult twins	GF C57BL/6J	N/A	Phenotype transfer of adiposity and obesity-associated metabolic features¹²
Obesity	Obese children and adolescents	GF Swiss Webster	N/A	Phenotype transfer of adiposity and increased fasting insulin¹⁸
Metabolome	Healthy adults	GF Swiss Webster and C57BL/6J	Dietary intervention by polysaccharide-deficient diet	Majority of metabolic features of donors were reflected in mice with the donor GM³⁹
Metabolome	Not specified	Antibiotic-treated A/J	N/A	GM from different donors resulted in different cecal metabolite profiles in recipient mice⁵
Infectious	Healthy adults	GF C57BL/6	Antibiotic disruption of GM and Clostridium difficile infection	Susceptibility to disease induction in the same way as SPF mice⁹
	Healthy adult	GF BALB/c	Challenge with Salmonella typhimurium	Colonization resistance toward infection¹¹
	Not specified	GF C3H/He	Challenge with enterotoxigenic Escherichia coli and ovalbumin	Protection against abrogation of oral tolerance, but only when born with microbiota²¹
Nutritional	Healthy adult	GF C57BL/6J	Dietary intervention by switch from low-fat to high-fat diet	Rapid responsiveness to dietary intervention²⁸
	Ten bacterial species selected from healthy GM	GF C57BL/6J	Dietary intervention by feeding refined macronutrients	Responsiveness to dietary intervention⁴⁰
	Healthy adults	GF Swiss Webster	Dietary prebiotic intervention	Mice with GM from different humans exhibited different responses to the dietary intervention⁴¹
	Healthy infants	GF Swiss Webster	Dietary intervention by infant formula ingredients	Responsiveness to dietary intervention⁷
Neuro- degenerative	Parkinson’s disease patients	GF overexpressing α-synuclein mice	Genetic susceptibility	Phenotype transfer of Parkinson’s disease traits⁴²
Neuro- degenerative	Multiple sclerosis patients	GF C57BL/6	Immunization with glycoprotein to induce experimental autoimmune encephalomyelitis	Phenotype transfer of CNS-specific autoimmunity¹³ Mice with patient and healthy control GM displayed different induction of regulatory T cells¹³
Oncology	Cancer patients	GF C57BL/6^22,23 GF C57BL/6N²⁴	Tumor engraftment and checkpoint inhibitor therapy	Phenotype transfer of drug efficacy towards checkpoint inhibitor therapy^22–24
Asthma	Asthmatic and healthy children	GF Swiss Webster	Ovalbumin-induced lung inflammation	Measurable inflammation in the model, though lower compared to mice with mouse GM¹⁶

N/A: not applicable; GF: germ-free; GM: gut microbiota.

For discovering associations between host phenotype and GM, animals with human GM aid in elucidating mechanistic pathways and possible new therapeutic targets. A famous example of phenotype transfer is that GF mice with GM from an obese twin gain more weight than mice having the GM from the lean counterpart twin.¹² Studies like this have helped improve our understanding of how the microbiome can be causal in the development of metabolic disorders. Linkage of GM composition to phenotype is not restricted to conditions in the gastrointestinal tract. GF mice colonized with GM from patients with multiple sclerosis (MS) had exacerbated symptoms of experimental autoimmune encephalitis compared with mice with GM from healthy controls, indicating a causative role of the GM in MS which was supported by fewer IL-10⁺ regulatory T cells (Tregs) in the mesenteric lymph nodes of these MS mice.¹³ The opportunity to unravel such immunological host–microbiota effects is the strongest argument for using animal models, yet the host–microbiota interface is the most questioned feature of the GM humanized mouse concept.

Challenges

Several reports describe an abnormal immunophenotype of mice with a human GM. The number of intraepithelial lymphocytes (IELs) was lower in GF mice with rat or human GM compared with mice colonized with a mouse GM. Furthermore, only the mouse GM was able to change histological characteristics of the IELs and epithelial cells.¹⁴ GF mice with human GM had low levels of CD4⁺ and CD8⁺ T cells and antimicrobial peptide in the small intestine.¹⁵ Splenocytes of GF mice with infant microbiota produced lower amounts of cytokines involved in Th1, Th2 and Treg responses.¹⁶ Comparable to GF mice, a human GM could not induce Tregs in the small intestine, whereas Tregs were higher in the colon compared with GF control mice.¹⁷ Hence, human-derived bacteria may have a higher affinity or colonization preference to the murine large intestine compared with the small intestine.

The immunological defects are hypothesized to be caused by lack of evolutionary adaptation to the host. It is well known that only a portion of human GM is successfully transferred to mice. In GF mouse experiments, the colonization efficiency typically varies between 44% and 70%,^15,18,19 though in one case it was as successful as 90%.²⁰ A study using antibiotic-treated mice reached a 57–68% recovery of bacterial genes in recipients compared with the donor sample.⁵ Mouse-to-mouse GM transfer is generally more successful, with a colonization efficiency up to 93%.¹⁵ Interestingly, rats may be better suited recipients of a human GM compared with mice. Wos-Oxley et al. transferred the same human GM to GF rats and mice and found that the colonization efficiency was significantly higher in the rats (76% versus 44%).¹⁹ Another study demonstrated that 75% of a human GM was established in GF rats.⁸

Table 2 summarizes examples of bacterial genera containing known health-beneficial species and strains which are difficult to establish in GF mice. Loss of specific bacteria is problematic when they are necessary for the outcome of the study, for example, for studying prebiotic metabolism by these bacteria. In other cases, the study concept is not compromised by the loss and seems to rely more on the complexity of the transferred GM or the presence of other organisms that were successfully established. For instance, induction of oral tolerance and protection against infection occurred in mice with human GM despite total loss of Bifidobacterium.²¹

Table 2.

Examples of human GM bacteria associated with human health that are showing variable colonization success in germ-free animal studies.

Organism	Colonization efficiency of organism		Recipient	Detection method	Reference
Bifidobacteriaceae	Completely lost 2 days post-colonization despite high abundance in inoculum (72.8%)	↓	Mouse	16S rRNA sequencing	⁷
Bifidobacterium spp.	Almost completely lost	↓	Mouse	16S rRNA sequencing	¹⁸
	Was transferred but to lower abundance than in inoculum	↓	Mouse	qPCR	⁴³
	Was not compared with the inoculum, but established well and at higher abundance than pigs with pig microbiota	↔	Pig	qPCR	³⁷
	Was not compared with the inoculum, but established in the mice and increased in response to feeding a high-bran diet	↔	Mouse	Culturing	⁴⁴
Faecalibacterium spp.	Almost completely lost	↓	Mouse	16S rRNA sequencing	¹⁸
	Established well in recipient rats	↔	Rat	DGGE + sequencing	⁴⁵
	Was not compared to the inoculum, but was established in mice	↔	Mouse	16S rRNA sequencing	²²
Lactobacillus spp.	Increased abundance from inoculum to recipient mice	↑	Mouse	qPCR	⁴³
	Disappeared 7 days post-colonization	↓	Mouse	Culturing	¹¹
	Disappeared 14 days post-colonization, but colonized long term if monocolonized prior to fecal transfer	↓	Mouse	qPCR	²⁹
Pseudobutyrivibrio spp.	Almost completely lost	↓	Mouse	16S rRNA sequencing	¹⁸

↑: increased abundance in recipient animals compared with the donor inoculum; ↓: decreased abundance in recipient animals compared with the donor inoculum; ↔: similar abundance in donor inoculum and recipients, or established in recipients but abundance not compared with inoculum.

Despite the immunological naivety characterizing mice harboring a human GM, the concept has demonstrated the ability to elicit differential and translationally relevant immune responses. Recently, GF mice with cancer patient GM replicated patient responses to checkpoint inhibitor immunotherapy through mechanisms hypothesized to happen via immunological stimulation by the transplanted microbiota.^22–24 Mice with GM from patients responding well to therapy recruited more CD4⁺ T cells²³ and CD8⁺ T cells^22,24 to the tumor microenvironment than mice with a non-responder GM. However, one of the studies found that only a portion of the GF mice with patient GM recapitulated the human responder phenotype, and these were the same mice whose GM was most different from the donor GM.²⁴ This may illustrate an element of luck and suggest that the desired outcome may simply be reached by including enough study replicates and hoping for the best. In a model of induced lung inflammation, mice with human GM mounted study-relevant and measurable inflammation, though it was lower than in mice with mouse GM and despite having reduced levels of Th1 and Th2 cytokines before the model was induced.¹⁶ Hence, if the read-out of the model is of a magnitude significant enough to be biologically meaningful, it may be less problematic that the immune baseline is below that of mice with mouse GM.

Can we overcome the challenges?

Physiological, anatomical and immunological abnormalities of GF mice are well documented and summarized elsewhere.²⁵ Most of these features are normalized after colonization with a complex GM. However, irrespective of whether the GM transplant is murine or human, a GF period in early life prior to colonization alters immunological shaping²⁶ and ability to confer colonization resistance against pathogens²¹ later in life. Hence, to allow for correct immunological development study mice should not be the parent ex-GF generation, but rather the offspring generations born with the GM.²¹ Sex also influences the GM profile. GM from a male donor established differently in male and female mice,²⁷ suggesting that alignment of donor and recipient sex may be necessary.

Few, if any, attempts to optimize the colonization efficiency in human-to-mouse GM transfer studies have been published. Yet, several procedural steps from collection of the donor material, handling, and storage to the transfer itself and the conditions following transfer may affect colonization efficiency. For practical reasons, feces is the most frequently used donor material, but a more truthful representation of the entire gastrointestinal tract in the donor sample might also enhance the diversity of the established microbiota. Transfer of fresh versus frozen material works equally well,^6,28 but the exact cryoprotection protocol, anaerobic conditions, single versus repeated gavage or the use of other administration forms may all influence transfer rate. For instance, a model-community of 10 bacterial strains from human feces was more successfully established in GF mice by separate monocolonizations and subsequent co-housing compared with one single administration of all 10 bacteria.³ Husbandry factors, diet probably being the most important one, are likely to impact the colonization. Genetic humanization, for example, of epithelial colonization factors, or humanization of immune cell populations are also interesting avenues yet to be explored. For obtaining an immunological phenotype similar to specific pathogen-free (SPF) mice, it may be necessary to add indigenous mouse bacteria to the human GM, as demonstrated with segmented filamentous bacteria.²⁹ Such hybrid approach combines the ecological community of a human GM with a more developed immune system and may thus be a better reflection of the reality.

What are the alternatives?

The major limitation of mice with human GM is the altered immunological shaping compared with mice harboring an SPF GM. Interestingly, SPF mice are criticized for exactly the same compared with their wild counterparts.^30–32 In our efforts to exclude unwanted microorganisms according to SPF health standards, the GM of SPF mice seem to have lost important immunomodulatory organisms. However, it complicates the picture that SPF rodents harbor different GM across animal institutions, which in turn elicit widely different phenotypes^33,34 and make generalizations impossible. Nevertheless, the question has been raised whether SPF mice are good models for humans at all.^30–32 We do not live in clean enclosures, and it is a natural part of our immunological education to be exposed to a variety of both beneficial and pathogenic microorganisms. Laboratory mice with a GM from wild mice have significantly improved disease resistance due to a better poised immunological state, and provide a provocative alternative to the too-clean SPF mice,³² and maybe also to mice with human GM. A large functional overlap between SPF GM and human GM has been shown,³⁵ and is an argument in favor of mouse cohorts with a co-evolved GM (wild or traditional SPF) that is functionally comparable to that of humans, yet able to induce immunocompetency in the hosts.

Rats have already been mentioned as potiential superiour recipients of human GM. Pigs are often proposed as more precise models of humans because of the highly comparable physiology. The GM of GF piglets colonized with human GM do indeed seem to have a good conformity with the donor.³⁶ In the same study, the authors did several rounds of GM administrations to the piglets over 10 days,³⁶ which may also have enhanced the colonization efficiency compared with rodent studies often relying on a single round of oral gavage. Another study found that a human GM induced immune parameters in GF piglets, that is, they had more CD4⁺ T cells and MHC class II expressing cells in the gut compared with piglets colonized with pig feces.³⁷ In this study, Bifidobacterium established well in the porcine hosts and may provide at least a partial explanation of the results.³⁷ Recently, a dog GM gene catalog was published and demonstrated that compared with the mouse and pig microbiome, the dog GM was most similar to the human GM,³⁸ implying that dogs may be a highly translationally relevant model system for human microbiome research. However, compared with mice, there are other limitations related to the use of rats and pigs and other animal models. Choice of model is in all cases a balance between practicalities, economics, what is accessible (for example, genetic modifications) and the expected translational value. In some cases, it might even not be an animal model that is best suited. For instance, for nutritional and metabolic studies merely considering the intestinal ecological habitat without regard to host–microbiome interaction and immune system development, in vitro gut simulator systems could be a valid alternative.

Conclusions

All models, including rodents colonized with human GM, have their pros and cons. It is essential to understand these thoroughly in order to obtain valid insights. Careful consideration should be given when immunological pathways are important for the model, whereas the humanized microbiota concept is probably more robust for nutritional studies and phenotype transfer studies. However, as exemplified throughout this review, there are still hypotheses to be tested that may help in optimizing the concept.

Footnotes

Acknowledgement

The author would like to acknowledge conversations with former colleagues at the University of Copenhagen and Taconic Biosciences.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

References

Krych

Hansen

CHF

Hansen

et al.

Quantitatively different, yet qualitatively alike: A meta-analysis of the mouse core gut microbiome with a view towards the human gut microbiome. PLoS One 2013; 8: e62578–e62578.

Mahowald

Rey

Seedorf

et al.

Characterizing a model human gut microbiota composed of members of its two dominant bacterial phyla. Proc Natl Acad Sci 2009; 106: 5859–5864.

Rezzonico

Mestdagh

Delley

et al.

Bacterial adaptation to the gut environment favors successful colonization: Microbial and metabonomic characterization of a simplified microbiota mouse model. Gut Microbes 2011; 2: 307–318.

Lundberg

Toft

August

et al.

Antibiotic-treated versus germ-free rodents for microbiota transplantation studies. Gut Microbes 2016; 7: 68–74.

Hintze

Cox

Rompato

et al.

Broad scope method for creating humanized animal models for animal health and disease research through antibiotic treatment and human fecal transfer. Gut Microbes 2014; 5: 183–191.

Ericsson

Personett

Turner

et al.

Variable colonization after reciprocal fecal microbiota transfer between mice with low and high richness microbiota. Front Microbiol 2017; 8: 196–196.

Nejrup

Licht

Hellgren

. Fatty acid composition and phospholipid types used in infant formulas modifies the establishment of human gut bacteria in germ-free mice. Sci Rep 2017; 7: 3975–3975.

Alpert

Sczesny

Gruhl

et al.

Long-term stability of the human gut microbiota in two different rat strains. Curr Issues Mol Biol 2008; 10: 17–24.

Collins

Auchtung

Schaefer

et al.

Humanized microbiota mice as a model of recurrent Clostridium difficile disease. Microbiome 2015; 3: 35–35.

10.

Siddharth

Holway

Parkinson

. A Western diet ecological module identified from the ‘humanized’ mouse microbiota predicts diet in adults and formula feeding in children. PLoS One 2013; 8: e83689–e83689.

11.

Wong

Hentges

Dougherty

. Adequacy of the human faecal microbiota associated mouse as a model for studying the ecology of the human intestinal tract. Microb Ecol Health Dis 1996; 9: 187–198.

12.

Ridaura

Faith

Rey

et al.

Gut microbiota from twins discordant for obesity modulate metabolism in mice. Science (80-) 2013; 341: 1241214–1241214.

13.

Cekanaviciute

Yoo

Runia

et al.

Gut bacteria from multiple sclerosis patients modulate human T cells and exacerbate symptoms in mouse models. Proc Natl Acad Sci USA 2017; 114: 10713–10713.

14.

Okada

Setoyama

Matsumoto

et al.

Effects of fecal microorganisms and their chloroform-resistant variants derived from mice, rats, and humans on immunological and physiological characteristics of the intestines of ex-germfree mice. Infect Immun 1994; 62: 5442–5446.

15.

Chung

Pamp

Hill

et al.

Gut immune maturation depends on colonization with a host-specific microbiota. Cell 2012; 149: 1578–1593.

16.

Arrieta

M-C

Sadarangani

Brown

et al.

A humanized microbiota mouse model of ovalbumin-induced lung inflammation. Gut Microbes 2016; 7: 342–352.

17.

Faith

Ahern

Ridaura

et al.

Identifying gut microbe-host phenotype relationships using combinatorial communities in gnotobiotic mice. Sci Transl Med 2014; 6: 220ra11–220ra11.

18.

Zhang

Bahl

Roager

et al.

Environmental spread of microbes impacts the development of metabolic phenotypes in mice transplanted with microbial communities from humans. ISME J 2017; 11: 676–690.

19.

Wos-Oxley

Bleich

Oxley

APA

et al.

Comparative evaluation of establishing a human gut microbial community within rodent models. Gut Microbes 2012; 3: 234–249.

20.

Quach

Collins

Parameswaran

et al.

Microbiota reconstitution does not cause bone loss in germ-free mice. mSphere 2018; 3: e00545–e00517.

21.

Gaboriau-Routhiau

Raibaud

Dubuquoy

et al.

Colonization of gnotobiotic mice with human gut microflora at birth protects against Escherichia coli heat-labile enterotoxin-mediated abrogation of oral tolerance. Pediatr Res 2003; 54: 739–746.

22.

Gopalakrishnan

Spencer

Nezi

et al.

Gut microbiome modulates response to anti-PD-1 immunotherapy in melanoma patients. Science 2018; 359(6371): 97–103.

23.

Routy

Le Chatelier

Derosa

et al.

Gut microbiome influences efficacy of PD-1-based immunotherapy against epithelial tumors. Science 2018; 359(6371): 91–97.

24.

Matson

Fessler

Bao

et al.

The commensal microbiome is associated with anti-PD-1 efficacy in metastatic melanoma patients. Science 2018; 359: 104–108.

25.

Bleich

Fox

. The mammalian microbiome and its importance in laboratory animal research. ILAR J 2015; 56: 153–158.

26.

Hansen

CHF

Nielsen

Kverka

et al.

Patterns of early gut colonization shape future immune responses of the host. PLoS One 2012; 7: e34043–e34043.

27.

Wang

Pang

et al.

Sex differences in colonization of gut microbiota from a man with short-term vegetarian and inulin-supplemented diet in germ-free mice. Sci Rep 2016; 6: 36137–36137.

28.

Turnbaugh

Ridaura

Faith

et al.

The effect of diet on the human gut microbiome: a metagenomic analysis in humanized gnotobiotic mice. Sci Transl Med 2009; 1(6): 6ra14–6ra14.

29.

Imaoka

Setoyama

Takagi

et al.

Improvement of human faecal flora-associated mouse model for evaluation of the functional foods. J Appl Microbiol 2004; 96: 656–663.

30.

Beura

Hamilton

et al.

Normalizing the environment recapitulates adult human immune traits in laboratory mice. Nature 2016; 532: 512–516.

31.

Reese

Kambal

et al.

Sequential infection with common pathogens promotes human-like immune gene expression and altered vaccine response. Cell Host Microbe 2016; 19: 713–719.

32.

Rosshart

Vassallo

Angeletti

et al.

Wild mouse gut microbiota promotes host fitness and improves disease resistance. Cell. Epub ahead of print 17 October 2017. DOI: 10.1016/j.cell.2017.09.016.

33.

Hart

Ericsson

Franklin

. Differing complex microbiota alter disease severity of the IL-10-/- mouse model of inflammatory bowel disease. Front Microbiol 2017; 8: 792–792.

34.

Ivanov

Atarashi

Manel

et al.

Induction of intestinal Th17 cells by segmented filamentous bacteria. Cell 2009; 139: 485–498.

35.

Xiao

Feng

Liang

et al.

A catalog of the mouse gut metagenome. Nat Biotechnol 2015; 33: 1103–1108.

36.

Pang

Hua

Yang

et al.

Inter-species transplantation of gut microbiota from human to pigs. ISME J 2007; 1: 156–162.

37.

Che

Pang

Hua

et al.

Effects of human fecal flora on intestinal morphology and mucosal immunity in human flora-associated piglet. Scand J Immunol 2009; 69: 223–233.

38.

Coelho

Kultima

Costea

et al.

Similarity of the dog and human gut microbiomes in gene content and response to diet. Microbiome 2018; 6: 72–72.

39.

Marcobal

Kashyap

Nelson

et al.

A metabolomic view of how the human gut microbiota impacts the host metabolome using humanized and gnotobiotic mice. ISME J 2013; 7: 1933–1943.

40.

Faith

McNulty

Rey

et al.

Predicting a human gut microbiota’s response to diet in gnotobiotic mice. Science 2011; 333: 101–104.

41.

Smits

Marcobal

Higginbottom

et al.

Individualized responses of gut microbiota to dietary intervention modeled in humanized mice. mSystems 2016; 1: e00098–16.

42.

Sampson

Debelius

Thron

et al.

Gut microbiota regulate motor deficits and neuroinflammation in a model of Parkinson’s disease. Cell 2016; 167: 1469–1480.

43.

Zeng

Yuan

et al.

Effects of age and strain on the microbiota colonization in an infant human flora-associated mouse model. Curr Microbiol 2013; 67: 313–321.

44.

Hirayama

Mishima

Kawamura

et al.

Effects of dietary supplements on the composition of fecal flora of human-flora-associated (HFA) mice. Bifidobact Microflora 1994; 13: 1–7.

45.

Licht

Madsen

Wilcks

. Selection of bacteria originating from a human intestinal microbiota in the gut of previously germ-free rats. FEMS Microbiol Lett 2007; 277: 205–209.

Humanizing the gut microbiota of mice: Opportunities and challenges

Abstract

Keywords

Introduction

The humanized gut microbiota concept

Opportunities

Challenges

Can we overcome the challenges?

What are the alternatives?

Conclusions

Footnotes

Acknowledgement

Declaration of Conflicting Interests

Funding

References