Contents



Preface

Many important advances have been made in human health-related studies. Indeed, gut microbial communities have been extensively analyzed and differences between healthy and diseased microbiomes have been determined. Studies of the effects of changes of diet, of antibiotic treatments, and of probiotics on the gut microbiome have been published. It was found that the human gut microbiome varies significantly from individual to individual, and longitudinal studies have shown the major effects of antibiotics as well as the time course of return to a "normal," healthy

Ethnic and geographical influences have been analyzed. While most studies focused on individuals in the Western world and their corresponding diet, comparisons with less accessible communities have been very informative. In particular, analyses of indigenous communities, never exposed to antibiotics, have illuminated the effects of their wide use. In other studies it was found, for example, that the use of antibiotics in early childhood can have life-long consequences, perhaps

Similar microbiome studies have been performed on human skin, oral cavities, and genitals. Different sites of the human body carry different niche-specific microbiota. Dry, moist, sebaceous, UV-exposed, and protected regions of skin all have different microbiota. The immense interpersonal variation precludes describing a "healthy" skin microbiome; however, one's skin microbiomes tend to be stable over time. Interestingly, the effects of hygiene products, soaps and deodorants, are apparently underwhelming and transient. Human skin and the oral cavity contain very rich and varied microbiomes with myriad species. In contrast, vaginal microbiomes in the posterior fornix tend to have a limited number of species, nearly monoclonal

Specific research has been devoted to human pathogens, their mechanisms of causing disease, and the potentials for their management and alleviation. For example, eczema, atopic dermatitis, is associated with overgrowth of *Staphylococcus aureus*. In contrast, psoriasis, another inflammatory skin disease, is not specifically

Interestingly, the richness and interpersonal differences in human microbiomes are equalized by the metabolic capabilities of such microbiomes. In other words, while the compositions of the microbiomes vary greatly, the overall metabolic processes, synthesis, and degradation of nutrients and other natural products do not vary much; different assemblies of microorganism can perform similar tasks.

The recent breakthrough in microbial studies has applied next-generation sequencing (NGS), a massive omics analysis, to the composition and structure of microbial communities. NGS can identify microbes without the need for their cultivation. Their mere presence can be ascertained and often quantitated, and even their metabolic capabilities of microbial constituents predicted. This

breakthrough led to an explosive growth in research on microbes.

microbiome.

predisposing to allergic and atopic sequelae.

associated with a particular microbiome.

lactobacilli environment.
