What is the Future of the Gut Microbiota-Related Treatment? Toward Modulation of Microbiota in Preventive and Therapeutic Medicine

INTRODUCTION The human body is colonized by a wide variety of micro-organisms, which are known to play an important role in regulation of metabolic functions and maintaining immune homeostasis. Instantaneously after birth, skin surface, oral cavity, and gut are settled by extensive range of microbes, mainly bacteria, but also archaea, fungi, viruses, and protozoa. Commonly called human microbiota, it consists of trillions of organisms from over 1000 species. The most abundant species are members of the phyla Bacteroidetes and Firmicutes. An important number of studies have been undertaken to determine if the gut microbiota is a promising target for clinical treatment or prevention. In the current issue of Frontiers in Medicine – Gastroenterology, Nagpal et al. paid close attention to the role of gut in health and disease. In their paper, they raise important questions and pay particular attention to ambiguities, which still remain to be elucidated to proper understanding of the complexity of human– microbe relationships. To better translate and apply current knowledge in clinical practice, answering the queries about compositional alterations in gut microbiome by diet or during diseases is necessary. ROLE OF GUT MICROBIOTA IN HEALTH AND DISEASE Bacterial diversity changes with age (1). As stated earlier, the adult gut ecosystem is dominated particularly by Firmicutes and Bacteroidetes phyla, but also by Actinobacteria, Proteobacteria, and Verrucomicrobia (2, 3); the anaerobic bacteria include Bifidobacterium spp and Faecalibacterium spp. It is important to emphasize that oxygentolerant bacteria, such as Lactobacillus spp. and members of Proteobacteria phylum may also appear in the gut, but in a low number. The population of aerobic bacteria is fluctuating over time and depends on diet and other environmental factors, such as hygiene, climate, geography, and ethnicity (4). The influence of nutrients on microbiome diversity was affirmed in the study by De Filippo et al. (5), in which Western diet in European children, high in animal protein and fat, caused reduction in short chain fatty acid-producing bacteria and increased the number of potentially pathogenic organisms in comparison to low animal protein diet and highcarbonate used by children in rural Africa. Nagpal et al. exposed the importance of diet in microbiota gentle alterations and the necessity of defining the ideal dietary macronutrients composition (ratios and types of carbohydrates, fats, and proteins). Changes in gut microbiota in various types of diseases, such as obesity, IBD, type 2 diabetes, and non-alcoholic fatty liver disease is another problem raised by Nagpal et al. Gut microbiota dysbiosis causes increased gut permeability, systemic inflammation, and insulin resistance. Recent studies showed that patients suffering from IBD harbor altered gut microbiota, especially a reduced bacteria diversity (6, 7). In line, a decreased number of the butyrate-producing bacteria Roseburia hominis and Faecalibacterium prausnitzii have been observed in ulcerative colitis patients in comparison to control individuals (8). Of note, gut microbiota dysbiosis and lower levels of butyrate-producing bacteria were also observed in diabetes type 2 patients (9).