Organ‐Specific Human Microbiomes and Dysbiosis: Mechanistic Links to Disease and Emerging Therapeutic Strategies

FIGURE 1. Systemic interactions between the human microbiome, microbial metabolites, and host regulatory pathways across body sites. Major microbial communities and microbiota‐derived metabolites (e.g., short‐chain fatty acids [SCFAs], trimethylamine N‐oxide [TMAO], tryptophan metabolites, neurotransmitters, lipopolysaccharide [LPS], indoxyl sulfate, and p‐cresyl sulfate) in different body sites are shown, highlighting the gut–brain, gut–heart, and gut–kidney axes involved in host regulation and disease. Metabolite signaling occurs through immune (cytokines, LPS), neural (vagus nerve, neurotransmitters), and endocrine–metabolic (circulatory and bile acid–mediated) pathways. Bidirectional interactions are impacted by host characteristics like immune state, the integrity of the epithelial barrier, genetics, and environmental exposures; routes are shown graphically to highlight key ideas rather than provide comprehensive mechanisms.

FIGURE 2. The human microbiome as a central regulator of health and disease. A balanced microbiome (eubiosis) is contrasted with dysbiosis to highlight key microbial components and lifestyle and environmental factors determining microbial balance, gut–organ axis interactions, and major disease outcomes associated with microbiome disruption. Importantly, the majority of the associations between microbiomes and diseases that are shown are associative correlations; causative contributions have only been proven in certain situations (e.g., certain infections and toxin‐mediated illnesses).

FIGURE 3. Microbiome‐based therapeutic strategies for restoring host health. Major microbiome‐targeted therapies, i.e., additive, subtractive, modulatory, and psychobiotic approaches, aimed at restoring microbial balance and supporting host physiological health are shown. Many modalities are still in early‐phase or preclinical stages, despite the fact that some (like FMT and antimicrobials) have entered clinical practice for specific indications. Widespread implementation is currently limited by regulatory frameworks, safety concerns, difficulties with standardization, and variations in host–microbiome responses.