What are the consequences of the disappearing human microbiota?

Abstract

The increase in allergic diseases that has occurred in developing countries in recent years has been attributed to a decrease in exposure to the microorganisms in the environment. Blaser and Falkow reflect that this increase, as well as the ongoing obesity epidemic and increased susceptibility to infectious disease, might instead be the result of changes in the human microbiota. Humans and our ancestors have evolved since the most ancient times with a commensal microbiota. The conservation of indicator species in a niche-specific manner across all of the studied human population groups suggests that the microbiota confer conserved benefits on humans. Nevertheless, certain of these organisms have pathogenic properties and, through medical practices and lifestyle changes, their prevalence in human populations is changing, often to an extreme degree. In this Essay, we propose that the disappearance of these ancestral indigenous organisms, which are intimately involved in human physiology, is not entirely beneficial and has consequences that might include post-modern conditions such as obesity and asthma.