From germ theory to germ therapy.

Germ theory of disease and Koch's postulates has been governing our understanding of the role of microbes in human health since 19th century. The discovery of Helicobacter pylori (H. pylori) and H. pylori associated diseases has typically represented the concept and framework of Koch's postulates. Eradication of H. pylori to prevent peptic ulcers recurrence and gastric cancer is the triumph of this microbiology paradigm. Advances of next generation sequencing provide great insight into the unculturable microbes and show trillions of microbes have evolved with human beings. Research into the microbiome-the microbial communities (microbiota) and the host environment that they inhabit-has changed our understanding about microbes in human health and disease. The gut microbiota, the largest reservoir of the microbiome in human, plays a critical role in our catabolic-metabolism and immunity. This review will show the changes of the view of microbes on human health. We will briefly discuss dysbiosis, the disruption of symbiotic relationship between the host and microbiota, and the associated diseases. This leads to an idea to manipulate the microbiota, either by restoring missing functions or by eliminating harmful functions, to prevent or treat a variety of diseases. Current evidences of two common germ therapies, fecal microbiota transplantation and probiotics, in treating diseases will be reviewed.