The collective community of bacteria, archaea, fungi, viruses and other microorganisms, along with their genomes, that live on and within the human body.
Explanation
The human microbiome encompasses trillions of microorganisms residing on the skin, in the gut, oral cavity, respiratory tract, urogenital tract and other surfaces. These communities establish shortly after birth, influenced by mode of delivery, diet, environment and host genetics, and evolve through life. Dominant bacterial phyla in the gut include Firmicutes and Bacteroidetes, with contributions from Actinobacteria and Proteobacteria; viral and fungal members add to the diversity. Microbiome organisms perform essential functions such as fermenting indigestible dietary fibres, synthesizing vitamins, breaking down xenobiotics, modulating immune system development and preventing colonization by pathogens through competitive exclusion and production of antimicrobial compounds. Differences in microbiome composition are associated with diet (plant versus animal-based), geographic region and antibiotic exposure. Disruptions to community structure, termed dysbiosis, have been linked to conditions including inflammatory bowel disease, obesity, type 2 diabetes, allergies and neurodevelopmental disorders, although causal relationships are still being unravelled. Modern sequencing and metagenomic approaches allow comprehensive surveys of microbiome diversity and functions, spurring interest in probiotics, prebiotics and faecal microbiota transplantation as interventions. Understanding the human microbiome provides insight into host–microbe mutualism and disease susceptibility.
Microbiome Diversity Across Body Sites
The gut microbiome harbours dense populations of Bacteroides, Faecalibacterium and Ruminococcus species that aid digestion and produce short-chain fatty acids. The skin microbiome varies by site; dry areas host Staphylococcus epidermidis and Corynebacterium species, whereas oily sites contain Cutibacterium acnes. The oral cavity supports Streptococcus mutans and Veillonella, which contribute to dental plaque and caries when imbalanced. Vaginal microbiota in many individuals are dominated by Lactobacillus species that maintain acidic pH and inhibit pathogens. Each niche provides unique resources and challenges, shaping microbial adaptation and community composition.
The human microbiome is a key component of human biology. Characterizing its members and their interactions with the host will continue to advance understanding of health, disease and therapeutic possibilities.
Related Terms: Microbiota, Dysbiosis, Commensal, Probiotic, Metagenomics