Our health and probably also our behaviors and mood depend not only on what we eat or what we do (lifestyle behaviors), but also on what we host. It is well established for decades that all vertebrates including humans are colonized by a wide array of bacteria, fungi, eukaryotic parasites and viruses, and that, at steady state (homeostasis), this community of microbes establishes a friendly mutual relationship with the host. The term microbiota was originally meant to represent an ecological community of commensals and potentially pathogenic microbes that live within our bodies, but it is now used interchangeably with the term microbiome which was initially meant to represent a collective genome of the microbiota. Although the number of microbes that live in or on our body was previously estimated to outnumber that of their hosts by 10 to 1, the latest estimate put the ratio to be closer to 1:1. On the other hand, their collective genomes (microbiome) outnumber those of the host by 100-200 times. It is not surprising therefore that these microbes not only provide the host with a variety of metabolic impact, but can also modulate tissue integrity and immune defense, all of which lead to a healthy ecosystem (symbiosis) that is unfavorable for colonization and invasion of pathogens. Microbiota is well known for its role in development and education of immune system. However, its link with diseases is less known and it is only recently that there is a surge of interest in the potential impact of microbiota on human health and disease. The diversity and composition of microbiota (healthy microbiota profile) are dynamics, depending not only on the host physical status, genotype and immune phenotype, but also on the environmental factors like diet, antibiotic usage and lifestyle behaviors. These environmental factors may adversely alter gut ecosystem (dysbiosis) that is frequently associated with increased susceptibility to infections as well as to non-communicable diseases like obesity, metabolic syndromes (e.g., diabetes and cardiovascular diseases), allergy and other inflammatory diseases. Emerging evidence from more recent studies also demonstrate the existence of a bidirectional communication route linking gut and microbiota with brain, thus suggesting that these microbes may play a role in neurological disorders as well as in host perception, behavior and emotional response. However, whether the observed alteration of the microbiota profile in these diverse conditions is the cause or the consequence of the disease remains to be established. These observations imply that it may be possible to design new strategies for the management of diseases by manipulating gut microbiota. The common practice now available is the use of probiotics to rehabilitate gut ecosystem. The microbiota-based therapeutics like fecal transplantation for the treatment of recurrent antibiotic-resistant Clostridium difficile infection is now under clinical trial and reported to be highly successful. In the next decade, we will probably see even more exciting approaches, for example, using advanced microbiota engineering technologies to create "intelligent" or "smart" bacteria for use in diagnosis, prevention, prediction and treatment of inflammatory diseases and possibly of some gastrointestinal cancers. The microbiota-based therapeutics together with personalized medicine may be the most accurate and optimal strategy for the future treatment of some difficult-to-manage diseases. However, many challenges remain to be solved before the translational potential of this new knowledge can be implemented clinically. In this review, I highlight some important recent developments and advances that contribute to our understanding in the role of microbiota in human health and disease and on how to best manipulate the microbiome to promote greater human health.
