I. 1 The Human Microbiota and Its Management – Clinical Frameworks

Your body is a microbial ecosystem; when its balance collapses, FMT aims not to kill a pathogen but to rebuild the whole community.

Building a New Life, One Microbe at a Time – Why This Handbook Exists

The scientific consensus now views the human body as an ecosystem in which microbes actively participate in digestion, immune regulation, and a wide range of metabolic processes extending far beyond the gastrointestinal tract [441]. This microbial community is vast: the human gut alone harbours approximately 3.8×10¹³ bacterial cells (approximately 1:1 with host cells) representing more than 1,000 species at the population level (at least 160 species coexisting in any individual) – their combined gene catalogue is roughly 150 times larger than the human gene complement [442], [443]. This community – the gut microbiota^[G] – is not a passive bystander in human health, but an active participant in processes including short-chain fatty acid production, bile acid metabolism, immune system education, neuroactive metabolite synthesis, and colonisation resistance^[G] against pathogens [111], [444], [445].

We now recognise that the human body is a superorganism: a complex, dynamically interacting ecosystem of human cells and trillions of microbial organisms. The disruption of this ecosystem – known as dysbiosis – is associated with a broad range of conditions extending well beyond gastrointestinal disease: metabolic syndrome, inflammatory bowel disease (Crohn's disease and ulcerative colitis), autoimmune conditions, mood disorders, and susceptibility to recurrent infections [446], [441]. The therapeutic implication is clear: restoring a disrupted system to a stable, functional state carries measurable clinical consequences [447].

The clinical objective of this guide is to support microbiota restoration in patients with dysbiosis-associated conditions, through faecal microbiota transplantation and structured lifestyle interventions connected to it. This handbook provides the scientific background, the still preliminary clinical protocols, and the practical tools for every stage of the process.

It is important to emphasise that this handbook is not promotional material, but a practical clinical and scientific reference. Every claim it contains is supported by peer-reviewed literature; references are provided at the end of each chapter. Recommendations are graded by evidence strength, and well-established guidance is explicitly distinguished from areas resting on emerging or preliminary evidence, which are nevertheless equally important. Where individual clinical judgement is required, this guide expressly directs the reader to consult their treating clinician.

Dysbiosis – The Ecological Imbalance Associated with Many Conditions

A disrupted microbiota, known as dysbiosis, is not a disease entity but an ecological imbalance – a functional state. Dysbiosis^[G] can manifest as:

• Reduced microbial diversity, impairing resilience and metabolic redundancy [114];
• Overgrowth of opportunistic species (e.g., Clostridioides difficile (formerly Clostridium difficile)) [001];
• Functional dysregulation, where microbial metabolic output is abnormal even if community composition appears superficially intact.

The causal direction between dysbiosis and the conditions listed above is not always established; in many cases they mutually reinforce one another: the disrupted bacterial matrix amplifies inflammation and metabolic dysfunction, which in turn further destabilises the microbiota [448]. Interrupting this cycle – through ecological restoration rather than symptom suppression alone – is the therapeutic rationale for FMT and the lifestyle interventions described in this guide.

It is worth introducing the contrasting concept: eubiosis. In this balanced state, the intestinal community maintains high species diversity, functional metabolic activity, and colonisation resistance – the capacity to prevent pathogen establishment through competitive exclusion^[G] and metabolite-mediated suppression [003]. Eubiosis (a balanced gut microbiota state characterised by high diversity and functional stability) is not a fixed endpoint or a defined composition; it is a dynamic functional state that each individual's microbiota can achieve through different routes, depending on genetic background, dietary patterns, and environmental history [114]. The interventions described in this guide aim to create the conditions under which eubiosis can re-emerge and be sustainably maintained.

In this context, the use of antibiotic therapy as a method of treating infection becomes a paradox: it eliminates pathogens while simultaneously further damaging the ecological infrastructure of colonisation resistance [449]. This paradox is most acute in recurrent C. difficile infection, where each antibiotic course suppresses the pathogen while removing the competitive microbial populations that would prevent its return – creating a cycle of recurrence that antibiotics alone cannot break [029]. FMT addresses this paradox directly: by reintroducing the ecological community, rather than simply targeting the pathogen.

FMT – Ecological Restoration, Not Just a Procedure

The FMT preparations – including phase-specific ones for hospital-based induction, CDI treatment, compatibility assessment, and consolidation – are designed to deliver diverse, screened donor microbial communities into the recipient's intestinal tract. The therapeutic effect of FMT, however, extends beyond bacterial recolonisation. The transplant carries metabolites, bacteriophages, immunomodulatory compounds, and the functional ecological relationships between species that confer resilience properties to the community [450]. We refer to this system as the microbiota matrix. This complexity explains why FMT restores a disrupted community more completely than probiotic supplementation: it delivers not isolated strains, but an integrated community with established competitive and metabolic dynamics [018], [156].

A successful transplant, however, is not merely about delivering microbes. It is also about creating and maintaining the favourable ecological conditions in which the incoming community can establish itself, remain competitive, and integrate [108]. This is the foundational logic of treatment protocols: the FMT intervention is embedded within a structured framework of compatibility assessment, induction, consolidation, and step-down phases, each optimising different aspects of ecological restoration. This protocol is described in detail in Chapter III of this guide.

The evidence base for FMT is strongest in recurrent C. difficile infection: the landmark randomised controlled trial documented an 81% cure rate after a single dose and 94% after a repeat dose [029]; the clinical guideline synthesising the randomised trials published since likewise recommends FMT to prevent further recurrence [447]. In chronic non-CDI conditions – including inflammatory bowel disease, metabolic syndrome, and functional gastrointestinal disorders – the evidence is more variable, and the treatment protocol correspondingly more complex, requiring longer consolidation and careful compatibility assessment [447]. Chapter III also details the scientific basis for these protocol differences.

The Exposome – The Environment That Determines Whether FMT Succeeds

Beyond capsules, the greatest determinant of microbiota colonisation success is the patient themselves – or more precisely, their exposome. The exposome^[G] is the totality of all environmental exposures an individual experiences throughout their lifetime: diet, physical activity, sleep, stress, medications, chemical exposures, and social environment [451], [452]. All of these factors can nourish or disrupt the microbial ecosystem. For example:

• Antibiotics eliminate pathogens but simultaneously disrupt the structural and functional integrity of the commensal microbial community, abolishing colonisation resistance alongside the target pathogen [449].
• Processed foods and dietary additives promote dysbiosis, while dietary fibre provides the fermentable substrate that sustains SCFA^[G]-producing taxa essential for mucosal health and immune regulation [238], [068].
• Chronic stress and poor sleep directly affect the gut-brain axis, modifying microbial composition through cortisol-mediated motility changes, increased epithelial permeability, and behavioural shifts in diet and physical activity [082], [061].

In the FMT context, the exposome has a specific and measurable clinical role: it defines the ecological conditions into which the donor community is introduced, and within which it must compete and establish. The environmental factors that support the incoming community – adequate dietary fibre, regular sleep, moderate physical activity, controlled stress, minimal unnecessary antibiotic exposure – favour durable FMT engraftment^[G]; the strongest direct human evidence currently concerns fermentable fibre intake [453], [454]. The exposome that works against the incoming community creates conditions favouring the resurgence of dysbiosis-promoting species and ecological regression.

Clinically, gradual correction of diet, sleep, stress, and medication load more reliably supports microbial resilience than abrupt or extreme interventions. The Exposome Assessment Questionnaire completed at the end of Phase 0 compatibility assessment (the D•E•M•I questionnaire, introduced in Chapter III.2) is the structured clinical instrument with which the treating clinician maps each patient's individual exposome profile before induction, identifying the barriers and enabling factors whose management can optimise the conditions for FMT. The chapters following the FMT protocol section of this guide (IV–XIV) describe each major exposome domain in detail, with specific recommendations ranked by evidence strength.

How to Use This Guide – The Structure of the FMT Recovery Programme

This guide follows the patient's clinical journey from the pre-FMT period through to the long-term maintenance of the restored ecosystem. It is not intended to be read from start to finish in a single sitting; it is a reference document, to be used chapter by chapter as treatment progresses. The table below summarises the guide's structure and its relationship to the clinical protocol phases.

Table 1 – Guide chapter structure and clinical protocol mapping # Chapters III.1–III.7 cover the complete FMT protocol; the exposome chapters (IV–XIV) are applied in parallel throughout the treatment period.

Four principles govern how to use this guide most effectively:

• Follow the protocol sequence. Read the Chapter III subsections in the order listed; do not skip ahead – each section builds on the previous one.
• Coordination between the clinical team and the patient is essential. This guide is a complement to clinical treatment, not a substitute. Where any discrepancy exists between this guide and any clinician's instructions, those instructions always take precedence. This guide is intended to support understanding of the rationale behind clinical decisions, not to enable independent clinical decision-making by any patient.
• Use of the Food and Symptom Diary from day one is recommended. The FMT protocol chapters reference the Food and Symptom Diary throughout, which is the primary clinical monitoring tool for every phase of treatment. Begin completing it before your first FMT dose and maintain it consistently. The quality of its entries directly affects the quality of clinical decisions made on your behalf.
• Introduce lifestyle changes incrementally. The exposome chapters (IV–XIV) describe multiple concurrent intervention domains. Do not attempt to change everything at once. Prioritise the changes your clinical team recommends, in the order they specify, based on your individual exposome profile. Each new behavioural pattern should be applied and consolidated within a 14–21 day integration window.

All other chapters are reference material. They are organised so that one can navigate to the topic most relevant to the current situation – whether that is a dietary question, a medication concern, or an environmental factor to be understood.

A Final Thought – Health Is an Ecosystem, Not a Battlefield

The key message of this handbook is simple: health is not the absence of microbes, but the presence of a balanced microbial life. The therapeutic model embodied in this guide is ecological, not eliminative: rather than targeting the removal of pathogens, it restores the competitive community that makes pathogen establishment – and the transition of certain microbes into pathogenic states – impossible; rather than suppressing symptoms through pharmacological agents alone, it rebuilds the ecological infrastructure from which sustained remission can lastingly emerge. This is not a rejection of conventional medicine, but an extension of human biology into its ecological dimension.

Dysbiosis is not associated with a single disease – it is linked to many conditions, though the strength of evidence and causal relationships differ considerably by indication. Microbiota restoration is not about eliminating what is harmful, but about rebuilding what is beneficial. The FMT protocol, exposome interventions, and lifestyle guidance all serve this ecological purpose.

With this guide, FMT treatment, and deliberate lifestyle interventions, we are not merely treating a disease. We are creating the conditions for a more resilient and more diverse gut microbial community to emerge. The chapters that follow describe each step of this work.

Chapter III.6 – Warning Signs: Information to be read before administering the first dose. Which symptoms require immediate contact between physician and patient.

Chapter XVIII.4 – Food and Symptom Diary: To be completed starting from Day 1 of Phase 0; a tool for monitoring the patient. The data directly influences the selection of the appropriate donor material and clinical decision-making.

Chapter XVIII.6 – Priority Guide: Information to be reviewed at the beginning of each treatment phase. Lists the three most important items for that phase.

References

[001] Seekatz A, Safdar N, Khanna S. The role of the gut microbiome in colonization resistance and recurrent. Therapeutic advances in gastroenterology. 2022. Link

Colonization resistance of the gut microbiota and FMT therapy in rCDI — A healthy microbiota inhibits C. difficile colonization (nutrient competition, bile acids, SCFAs, bacteriocins). Antibiotics → dysbiosis → CDI. FMT restores diversity. Monoclonal antibodies do not treat dysbiosis.

[003] Reed AD, Theriot CM. Contribution of Inhibitory Metabolites and Competition for Nutrients to Colonization Resistance against Clostridioides difficile by Commensal Clostridium**. Microorganisms. 2021. Link

This review examines how commensal *Clostridium* species mediate colonization resistance against C. difficile. Commensal *Clostridia* modify primary bile acids into secondary bile acids that suppress C. difficile spore germination and vegetative outgrowth. They additionally produce antimicrobial peptides and short-chain fatty acids that directly inhibit C. difficile and compete for limiting nutrients such as proline, important for C. difficile growth via Stickland fermentation. Loss of commensal *Clostridia* after broad-spectrum antibiotics is a key mechanistic step toward CDI susceptibility. The authors conclude from this that new therapies against CDI are urgently needed; the clinical validation of defined *Clostridium* consortia comes not from this review but from the VE303 phase 2 trial [56].

[018] Suez J, Zmora N, Zilberman-Schapira G, Mor U, Dori-Bachash M et al. Post-Antibiotic Gut Mucosal Microbiome Reconstitution Is Impaired by Probiotics and Improved by Autologous FMT. Cell. 2018. Link

Human and mouse study of what happens to the gut mucosal microbiome after a course of antibiotics. Three routes were compared: spontaneous recovery, an 11-strain probiotic preparation, and autologous faecal transplantation, that is, return of the person's own flora frozen before the antibiotic. The probiotic colonised the mucosa but delayed the return of the indigenous microbiome and of host mucosal gene expression, and the difference persisted for months. Autologous transplantation, by contrast, produced near-complete recovery within days. Conclusion: after antibiotics a probiotic is not a neutral supplement but may slow the return of the native flora; it is a full microbiota graft that replaces the missing community.

[029] van Nood E, Vrieze A, Nieuwdorp M, Fuentes S, Zoetendal EG, de Vos WM, Visser CE, Kuijper EJ, Bartelsman JF, Tijssen JG, Speelman P, Dijkgraaf MG, Keller JJ. Duodenal infusion of donor feces for recurrent Clostridium. difficile. The New England Journal of Medicine. 2013. Link

The first randomised controlled trial comparing faecal microbiota transplantation with standard antibiotic therapy in recurrent *Clostridioides difficile* infection. Patients were assigned to three arms: donor faeces given through a duodenal tube after a short course of vancomycin, vancomycin alone, or vancomycin with bowel lavage. The trial was stopped early because the difference was so large: in the transplantation arm 81 percent of patients were cured after the first infusion and 94 percent including repeat infusions, against 31 and 23 percent in the two vancomycin arms. After treatment the diversity of the patients' faecal flora came to resemble that of the donors. This paper turned microbiota transplantation into an evidence-based treatment and is the starting point for the dosing regimen of the present protocol.

[061] Benedict C, Vogel H, Jonas W et al. Gut microbiota and glucometabolic alterations in response to recurrent partial sleep deprivation in normal-weight young individuals. Mol Metab. 2016. Link

Randomized within-subject crossover study in 9 normal-weight men comparing two nights of partial sleep deprivation (PSD; 02:45–07:00) with two nights of normal sleep (22:30–07:00) under standardized in-lab meal and exercise conditions. Faecal samples were collected and oral glucose tolerance was tested. The study assessed whether short-term sleep loss alters gut microbiota composition and metabolic function, providing early human evidence linking sleep restriction to acute microbiota shifts and insulin resistance.

[068] Desai MS, Seekatz AM, Koropatkin NM et al. A dietary fiber-deprived gut microbiota degrades the colonic mucus barrier and enhances pathogen susceptibility. Cell. 2016. Link

In gnotobiotic mice colonised with a synthetic human gut microbiota, chronic or intermittent dietary fibre deficiency caused the microbiota to use host-secreted mucus glycoproteins as a nutrient source, eroding the colonic mucus barrier. Combined fibre deprivation and a mucus-eroding microbiota allowed greater epithelial access and lethal colitis by the mucosal pathogen Citrobacter rodentium. The findings link diet, microbiome and intestinal barrier dysfunction and identify dietary fibre as a key barrier-protective factor exploitable for therapeutic strategies.

[082] Kelly JR, Kennedy PJ, Cryan JF, Dinan TG, Clarke G, Hyland NP. Breaking down the barriers: the gut microbiota, intestinal permeability and stress-related psychiatric disorders. Front Cell Neurosci. 2015. Link

The gut-brain axis is positioned as a critical node in stress-related psychiatric disorders, with the gut microbiome modulating brain development, function and behavior through immune, endocrine and neural pathways. Preclinical evidence implicates impaired intestinal barrier function — the so-called leaky gut — as a key mediator linking dysbiosis to chronic low-grade inflammation and disorders such as depression. The gut microbiome regulates intestinal permeability via short-chain fatty acids, mucin production and tight-junction signaling. The review argues that targeting microbiota-driven barrier integrity may offer mechanistic and therapeutic insight into stress-related psychiatric disease.

[108] Smillie CS, Sauk J, Gevers D, Friedman J, Sung J, Youngster I, Hohmann EL, Staley C, Khoruts A, Sadowsky MJ, Allegretti JR, Smith MB, Xavier RJ, Alm EJ. Strain Tracking Reveals the Determinants of Bacterial Engraftment in the Human Gut Following Fecal Microbiota Transplantation. Cell Host Microbe. 2018. Link

Strain-level tracking after FMT: the authors examined what determines whether a given donor strain engrafts in the recipient. The strongest predictor is the **composition of the recipient's own community** — a strain engrafts when a relative is already present, or when a free ecological niche exists; donor strain richness and strain abundance also matter. Engraftment therefore follows ecological rules rather than chance, and is modifiable from the recipient's side. Important: the paper describes strain-level determinants; it does not prove fibre availability as a modifiable factor in an RCT.

[111] Koh A, De Vadder F, Kovatcheva-Datchary P, Bäckhed F. From Dietary Fiber to Host Physiology: Short-Chain Fatty Acids as Key Bacterial Metabolites. Cell. 2016. Link

Mechanistic review of short-chain fatty acids (SCFAs), produced by bacterial fermentation of dietary fibre. Fermentable fibre is the primary energy source for the colonic microbiota; the main fermentation products are **acetate, propionate and butyrate**. **Butyrate is the principal energy substrate of colonocytes**; SCFAs also influence barrier integrity, immune function and, once in the circulation, host metabolism, partly via G-protein-coupled receptors (GPR41/43) and histone deacetylase inhibition. This entry is the source for the textbook-level claims of III.2 (S-0302-01, -02). Important: a **review**, not original experimental data.

[114] Lozupone CA, Stombaugh JI, Gordon JI, Jansson JK, Knight R. Diversity, stability and resilience of the human gut microbiota. Nature. 2012. Link

Review of the diversity, stability and resilience of the human gut microbiota. Applying ecological concepts to the gut, the authors argue that **species richness and evenness** are key indicators of a community's capacity to withstand perturbation: functional redundancy in a diverse community means the loss of a single taxon is less disruptive. They discuss the concept of dysbiosis and the association of low-diversity states with several diseases. Important: a **review** providing an ecological framework; it does not treat CDI separately and offers no causal evidence.

[156] Ianiro G, Puncochar M, Karcher N, Porcari S, Armanini F, Asnicar F, Segata N. Variability of strain engraftment and predictability of microbiome composition after fecal microbiota transplantation across different diseases. Nat Med. 2022. Link

Integrated shotgun-metagenomic meta-analysis of 226 triads (donor, pre-FMT and post-FMT recipient) across eight different disease types, using improved strain profiling. The key finding: **recipients with higher donor-strain engraftment were more likely to achieve clinical success** after FMT (P=0.017). Engraftment depends on the donor, the delivery route (multi-route — e.g. capsule plus colonoscopy together — gives higher engraftment) and the recipient (higher in antibiotic-treated infectious-disease recipients than in antibiotic-naive noncommunicable-disease patients); Bacteroidetes and Actinobacteria species engraft better. This entry is the source for the IV.3 claim that, because of donor-dependent engraftment variability, an alternative donor lot (LOT switch) can improve the outcome. **LIMITATION:** an observational meta-analysis across eight disease types (not CDI alone), measuring association; it did not study product-LOT switching as such.

[238] Chassaing B, Compher C, Bonhomme B et al. Randomized Controlled-Feeding Study of Dietary Emulsifier Carboxymethylcellulose Reveals Detrimental Impacts on the Gut Microbiota and Metabolome. Gastroenterology. 2022. Link

16-subject controlled-feeding RCT in human volunteers. Diet containing carboxymethylcellulose (CMC, E466) emulsifier altered gut microbiota composition within 11 days, decreased microbial diversity and fermentation metabolite levels, and two participants showed signs of bacterial encroachment into the mucus layer. First human evidence that CMC at approved daily exposure levels has detrimental microbiological effects.

[441] Lynch SV, Pedersen O. The Human Intestinal Microbiome in Health and Disease. N Engl J Med. 2016. Link

Lynch and Pedersen provide a comprehensive New England Journal of Medicine review on the human intestinal microbiome in health and disease. They summarize the composition and stability of the adult microbiota, the major bacterial phyla (Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria), and the impact of host genetics, diet, antibiotics and birth mode on community structure. Mechanistic sections cover short-chain fatty acid production, bile acid metabolism, immune education, and barrier maintenance. Disease associations are reviewed for IBD, obesity, type 2 diabetes, atherosclerosis, allergy, and Clostridioides difficile infection. The article frames the microbiome as a tractable therapeutic target via diet, prebiotics, probiotics and fecal microbiota transplantation.

[442] Sender R, Fuchs S, Milo R. Are We Really Vastly Outnumbered? Revisiting the Ratio of Bacterial to Host Cells in Humans. Cell. 2016. Link

Sender, Fuchs and Milo recalculated the widely cited 10:1 bacteria-to-human-cell ratio. Using updated data for a 70 kg reference man, they estimated about 3.8×10^13 bacteria versus about 3.0×10^13 human cells — a ratio close to 1:1 rather than 10:1, which a single defecation can shift in favour of human cells. The paper corrected a decades-old myth in microbiome science.

[443] Qin J, Li R, Raes J et al. A human gut microbial gene catalogue established by metagenomic sequencing. Nature. 2010. Link

Illumina-based metagenomic sequencing of faecal samples from 124 European individuals (576.7 Gb of sequence) yielded a catalogue of 3.3 million non-redundant microbial genes, approximately 150-fold larger than the human gene complement. Genes were largely shared across individuals, with over 99% bacterial origin. The cohort harboured an estimated 1,000–1,150 prevalent bacterial species, each individual carrying at least 160 species. The study defines a minimal gut metagenome and a minimal gut bacterial genome based on functions present in all individuals and most bacteria. Findings establish a foundational reference for the genetic potential of the human gut microbiota.

[444] Ridlon JM, Kang DJ, Hylemon PB, Bajaj JS. Bile acids and the gut microbiome. Curr Opin Gastroenterol. 2014. Link

Review of the bile acid–gut microbiome axis in health and disease, focusing on two major microbial pathways for bile salt degradation and the impact of bile acid composition on microbiota and host physiology. Bile acid pool size is now recognized as a function of microbial bile acid metabolism. Bile acids regulate the microbiome at the highest taxonomic levels and act as signalling hormones, with emerging evidence implicating them in liver carcinogenesis. The review frames bile acids as bidirectional mediators of host–microbiome crosstalk.

[445] Cryan JF, O'Riordan KJ, Cowan CSM et al. The Microbiota-Gut-Brain Axis. Physiol Rev. 2019. Link

A comprehensive review (Cryan et al., Physiol Rev 2019) of the microbiota-gut-brain axis. It details the communication routes linking the gut microbiota and the brain, including the immune system, tryptophan metabolism, the vagus nerve and enteric nervous system, and microbial metabolites (short-chain fatty acids, branched-chain amino acids, peptidoglycans). The article surveys animal and human evidence for the axis's physiological and behavioral/neurological significance.

[446] Turnbaugh PJ, Ley RE, Hamady M, Fraser-Liggett CM, Knight R, Gordon JI. The Human Microbiome Project. Nature. 2007. Link

Strategic framework outlining the Human Microbiome Project's approach to characterizing the microbial components of the human genetic and metabolic landscape. The initiative aims to establish how microbiota contribute to normal physiology and predisposition to disease. Serves as the foundational programmatic statement for large-scale population-level microbiome research.

[447] Peery AF, Kelly CR, Kao D et al. AGA Clinical Practice Guideline on Fecal Microbiota-Based Therapies for Select Gastrointestinal Diseases. Gastroenterology. 2024. Link

AGA clinical practice guideline using the GRADE framework to address fecal microbiota-based therapies (conventional FMT, fecal microbiota live-jslm, fecal microbiota spores live-brpk) in adults with recurrent or severe-to-fulminant Clostridioides difficile infection, IBD/pouchitis, and IBS. The panel issued 7 recommendations. In immunocompetent adults with recurrent CDI, the AGA suggests selective use of fecal microbiota-based therapies after standard-of-care antibiotics to prevent further recurrence. Provides framework guidance integrating FDA-approved products with conventional FMT.

[448] Thaiss CA, Zmora N, Levy M, Elinav E. The microbiome and innate immunity. Nature. 2016. Link

Mechanistic review of how the intestinal microbiome integrates environmental inputs (diet) with genetic and immune signals to influence host metabolism, immunity, and infection response. Haematopoietic and non-haematopoietic innate immune cells at the host–microbiome interface sense microorganisms and their metabolites, translating these signals into physiological responses and microbial ecology regulation. Disruption of this innate immune–microbiota communication is implicated in complex disease pathogenesis. The review frames the microbiome as a central signalling hub coordinating host defence and homeostasis.

[449] Dethlefsen L, Relman DA. Incomplete recovery and individualized responses of the human distal gut microbiota to repeated antibiotic perturbation. Proc Natl Acad Sci USA. 2011. Link

This longitudinal study examined the distal gut microbiota of three individuals over 10 months spanning two courses of ciprofloxacin, analyzing 1.7 million 16S rRNA sequences from 52-56 samples per subject. Interindividual variation dominated; baseline within-subject communities were stable over months. Ciprofloxacin profoundly reduced diversity and shifted composition within 3-4 days of initiation, with incomplete and individual-specific recovery. The findings characterize gut microbiota resilience and the durable disruption caused by repeated fluoroquinolone exposure.

[450] Zuo T, Wong SH, Lam K et al. Bacteriophage transfer during faecal microbiota transplantation in Clostridium difficile infection is associated with treatment outcome. Gut. 2018. Link

Investigation of enteric virome alterations in 24 CDI subjects and 20 healthy controls using ultra-deep metagenomic sequencing of virus-like particles plus 16S rRNA bacterial profiling. Nine CDI patients treated with FMT and five treated with vancomycin were longitudinally assessed for virome and bacteriome changes in relation to treatment response. The data link viral transfer during FMT — particularly bacteriophages — with clinical resolution of CDI, suggesting that phage transfer contributes to the therapeutic effect beyond bacterial engraftment alone.

[451] Wild, C. P. Complementing the Genome with an 'Exposome': The Outstanding Challenge of Environmental Exposure Measurement in Molecular Epidemiology. Cancer Epidemiol Biomarkers Prev. 2005. Link

Wild's seminal 2005 Cancer Epidemiology, Biomarkers and Prevention commentary introduces the concept of the 'exposome' to complement genomic measurement in molecular epidemiology. He argues that lifetime environmental exposures, including diet, lifestyle, infections, pollutants and endogenous processes, are as important as the genome in determining disease risk, but are systematically under-measured. The article calls for technologies and study designs capable of capturing exposures across the life course with sensitivity comparable to high-throughput genomics. Wild outlines internal, specific-external and general-external exposome domains. The concept has since shaped large cohort studies and biomarker-based exposure assessment, including microbiome-related work.

[452] Rappaport SM, Smith MT. Environment and Disease Risks. Science. 2010. Link

Conceptual statement arguing that a new epidemiological paradigm is required to assess how lifetime cumulative exposure to environmental factors affects chronic disease risk. Calls for systematic exposome-level analysis beyond single-exposure designs.

[453] Teigen LM, Hoeg A, Zehra H, Vaughn BP. Nutritional optimization of fecal microbiota transplantation in humans: a scoping review. Gut Microbes. 2025. Link

Human scoping review on nutritional optimization of FMT: recipient fiber intake and fermentable substrate availability influence engraftment; even short fiber-free periods (e.g., NPO) may impair FMT success in the immediate post-FMT period, because the incoming donor community needs fermentable substrate to colonize.

[454] Gogokhia L, Tran N, Grier A, Nagayama M, Xiang G, Funez-dePagnier G, Lavergne A, Ericsson C, Ben Maamar S, Zhang M, Battat R, Scherl E, Lukin DJ, Longman RS. Donor composition and fiber promote strain engraftment in a randomized controlled trial of fecal microbiota transplant for ulcerative colitis. Med. 2025. Link

The MINDFUL randomized, double-blind, placebo-controlled trial assigned 27 patients with mild-to-moderate ulcerative colitis to a single FMT or placebo, with or without psyllium fibre supplementation, over 8 weeks. FMT induced clinical response, remission and endoscopic improvement versus placebo (p < 0.05). Fibre supplementation did not improve clinical outcomes, but strain-level metagenomic analysis showed that donor community composition together with recipient fibre intake shaped donor-strain engraftment. This is among the first randomized human evidence that post-procedure dietary (exposome) factors directly influence FMT engraftment, while showing that improved engraftment does not automatically translate into better clinical outcomes. ClinicalTrials.gov: NCT03998488.