Probiotics, prebiotics, and synbiotics: gut and beyond

Abstract

The human intestinal tract has been colonized by thousands of species of bacteria during the coevolution of man and microbes. Gut-borne microbes outnumber the total number of body tissue cells by a factor of ten. Recent metagenomic analysis of the human gut microbiota has revealed the presence of some 3.3 million genes, as compared to the mere 23 thousand genes present in the cells of the tissues in the entire human body. Evidence for various beneficial roles of the intestinal microbiota in human health and disease is expanding rapidly. Perturbation of the intestinal microbiota may lead to chronic diseases such as autoimmune diseases, colon cancers, gastric ulcers, cardiovascular disease, functional bowel diseases, and obesity. Restoration of the gut microbiota may be difficult to accomplish, but the use of probiotics has led to promising results in a large number of well-designed (clinical) studies. Microbiomics has spurred a dramatic increase in scientific, industrial, and public interest in probiotics and prebiotics as possible agents for gut microbiota management and control. Genomics and bioinformatics tools may allow us to establish mechanistic relationships among gut microbiota, health status, and the effects of drugs in the individual. This will hopefully provide perspectives for personalized gut microbiota management.

Figure 1

The Human Body and number of bacteria present in the total microflora.

Figure 2

The complex web of gut microbiota contributions to host physiology. Different gut microflora components can affect many aspects of normal host development, while the microbiota as a whole often exhibits functional redundancy. Members of the microbiota are shown in gray, with their components or products of their metabolism. Their effects on the host at the cellular or organ level are shown in white. Black ellipses represent the affected host phenotypes. Only some examples of microbial members/components contributing to any given phenotype are shown. AMP: antimicrobial peptides; DC: dendritic cells; Gm−: gram negative; HPA: hypothalamus-pituitary adrenal; Iap: intestinal alkaline phosphatase; PG: peptidoglycan; PSA: polysaccharide A. Extracted from: Phys Rev 2010 Sekirov et al.

Figure 3

Diseases influenced by gut microbial metabolism. The variety of systemic diseases that are directly influenced by gut microbial metabolism and its influence on other mammalian pathways, such as the innate immune system, are shown. Specifically highlighted are the metabolic pathways involved in drug metabolism and obesity that are directly influenced by the gut microbial content. Ags, antigens; C. bolteae, Clostridium bolteae; DCs; dendritic cells; SCFA, short-chain fatty acid; TLR, toll-like receptor. Kinross et al. Genome Medicine 2011 3:14.