Transmission of the gut microbiota: spreading of health

Key Points The human intestinal microbiota is dominated by anaerobic health-associated bacteria that are established and maintained in individuals through host-to-host transmission. The transmission process incorporates excretion from a host in faecal matter, survival and persistence in the external environment, and concludes with ingestion and subsequent colonization of a new host. Studies of the routes of transmission of intestinal pathogens provide a useful framework to better understand intestinal commensal transmission. Both share some common transmission features, such as the use of the faecal–oral transmission route and similar survival mechanisms to persist in the external environment. Environmental survival mechanisms that are used by the intestinal microbiota once expelled by a host include sporulation, aerotolerance and entering a viable but non-culturable (VBNC) dormancy state. For anaerobic bacteria, these mechanisms protect against harmful oxygen, and in the case of sporulation and VBNC states, can provide varying resistance against other environmental conditions, such as desiccation and a lack of nutrients. Reservoirs are a source or a sink for bacteria during transmission. Other people in the community are the principal reservoirs of intestinal bacteria, but food, water, animals and the built environment may also facilitate transmission. Transmission of commensal bacteria may be disrupted by human sanitation practices, through the use of antibiotics or a long-term change in diet, which can eliminate species within an individual thereby preventing their onward transmission. Direct interventions to restore a depleted microbiota, such as faecal microbiota transplantation (FMT), are effective in some cases. A greater general awareness of the transmission of the commensal microbiota is facilitated by technological advances in different disciplines, including microbiology, bioinformatics and genomics. Fostering the transmission of commensal bacteria between people through the maintenance of a healthy lifestyle and the discerning use of antibiotics and sanitation processes may promote human health. The transmission of commensal intestinal bacteria between humans could promote health by establishing, maintaining and replenishing microbial diversity in the microbiota of an individual. In this Review, Browne and colleagues discuss the mechanisms and factors that influence host-to-host transmission of the intestinal microbiota. Transmission of commens