Transmission of the gut microbiota: spreading of health

Abstract

Transmission of commensal intestinal bacteria between humans could promote health by establishing, maintaining and replenishing microbial diversity in the microbiota of an individual. Unlike pathogens, the routes of transmission for commensal bacteria remain unappreciated and poorly understood, despite the likely commonalities between both. Consequently, broad infection control measures that are designed to prevent pathogen transmission and infection, such as oversanitation and the overuse of antibiotics, may inadvertently affect human health by altering normal commensal transmission. In this Review, we discuss the mechanisms and factors that influence host-to-host transmission of the intestinal microbiota and examine how a better understanding of these processes will identify new approaches to nurture and restore transmission routes that are used by beneficial bacteria.The human intestinal microbiota is one of the most densely populated microbial communities known to exist1. This community has important metabolic and protective roles in human health through metabolizing indigestible carbohydrates, producing vitamins, preventing infection by pathogenic bacteria and modulating host immune responses2. Bacteria form the majority of the microbial biomass in the human gastrointestinal microbiota and they carry out the majority of the metabolic activities2,3. Most of the bacteria in the gastrointestinal tract reside in the large intestine, with the rest found primarily in the small intestine and stomach4. The majority of these bacteria belong to two main phyla -the Bacteroidetes and Firmicutes. These phyla, together with the Proteobacteria, Actinobacteria, Synergistetes and Fusobacteria, contain almost all of the bacterial species found in the human gastrointestinal tract5-7. Most of these species are obligate anaerobes; however, the extent of aerotolerance varies among species in the Actinobacteria and Proteobacteria phyla8,9. Despite their abundance in the human gastrointestinal tract, these Correspondence to T.D.L. tl2@sanger.ac.uk. Competing interests statementThe authors declare no competing interests. Publisher's noteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Europe PMC Funders Group Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts species represent only a small subset of all of the bacterial taxa on Earth10. Furthermore, many of these bacterial taxa are not found replicating outside of the intestinal environment, which reflects their adaptation to this specific niche11,12.The factors that determine the optimal microbial community of an individual at any point in time are varied and include age, host genetics, diet and the local environment. Therefore, a core 'healthy' microbiota that is common to all individuals does not exist. Furthermore, the distinction between health-associated commensal bacteria and harmful pathogenic bacteria is not always clear, as some bacterial species can promote health or ca...

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