Review/Oorsig Volume 23, Issue 01 - Page 12

Oorsig/Review these microorganisms and host cells were long considered only from a pathogenic point of view because toxins invade the gut mucosa and translocate, disseminate, and cause systemic infections [10]. However, no attention was paid to the majority of gut microorganisms and their relationship with host health. Several studies have reported beneficial interactions between the commensal microbiota and the human body and have indicated that the microbiota acts as a real partner. A deeper understanding of the gut microbiota and its role is necessary for future healthcare strategies. In this regard, extensive study of the potential use of selected probiotic bacteria species and their strains is desperately needed for the prevention and treatment of numerous human and animal diseases [11–14]. The relationship between health and the composition of the gut microbiota has raised interest in the modulation of the gut microbiota by administration of probiotic species for the prevention of some diseases in humans and animals. This review focuses on the gut microbiota and several probiotic species that have been extensively studied in the modulation of the gut microbiota and prevention of degenerative diseases. 2. Gut Microbiota The term “gut microbiota” was first introduced to the scientifc community by Joshua Lederberg who called it “the ecological community of commensal, symbiotic, and pathogenic microorganisms that literally share our body space and have been all but ignored as determinants of health diseases” [31]. The human body consists of trillions of microbes, mostly within the gastrointestinal tract (i.e., the small intestine and colon). Using a 70 kg man as a reference, 3.8 × 1013 microbes are reported to have a total weight of 0.2 kg [32]. The gut microbiota can ferment nondigestible carbohydrates, which are well known as prebiotics, including fructooligosaccharide, oligofructose, inulin, galactose, and xylose, that contain oligosaccharides to fulfll energy requirements. The microbes in the host body have a significant influence on the metabolism, physiology, and immune development and function, whereas symbiotic functions include the synthesis of vitamins, protection from pathogenic colonization as a regulatory immune system via modulation of gastrointestinal hormone release function, and regulation of brain behavior in terms of neuronal signalling [33–38]. Te improvement of culture- independent and molecular high-throughput techniques favour the identification of previously 12 unknown bacteria, which would provide novel insights into the functional capacity and compositional diversity of some of the fecal microbiota. In addition, several studies have suggested that disorders such as colorectal cancer, inflammatory bowel disease (IBD), alcoholic and nonalcoholic fatty liver diseases, obesity, type 2 diabetes, oxidative stress–related disease, and immune-mediated diseases are associated with disease-specific dibiotic of altered microbiota compositions [15, 39–43]. Modification of the gut microbiota has thus gained more attention as a potential treatment for several diseases in humans and animals. 3. Modulation of Gut Microbiota and Probiotic Species The gut microbiota includes bacteria, fungi, archaea, protozoa, and viruses that interact with the host and each other to affect the host’s physiology and health [44]. The gut bacteria play significant roles in human health, including vitamin B synthesis, improvement in digestion, and promotion of angiogenesis and nerve function [45]. In addition, modification of the gut microbiota can be harmful when the gut ecosystem undergoes severe abnormal changes. The bacterial species found in the human gut microbiome include mostly three phyla: Bacteroidetes (Porphyromonas, Prevotella), Firmicutes (Ruminococcus, Clostridium, and Eubacteria), and Actinobacteria (Bifdobacterium). Lactobacilli, Streptococci, and Escherichia coli are found in small numbers in the gut. However, alteration of the gut microbiota composition can lead to multiple diseases in humans and animals [21, 22, 28, 30]. Current evidence supports a link between the activity and composition of the gut microbiota and human health and disease. Furthermore, the gut microbiota composition is likely to affect many organ systems, including the cardiovascular, neural, immune, and metabolic systems. The gut microbiota composition is altered in many disease states, such as cardiovascular disease, cancer, malignancy, type 2 diabetes mellitus, obesity, colitis, asthma, psychiatric disorders, inflammatory disorders, disorders of the gut- brain axis, and numerous immune disorders [15, 40, 41, 46–48]. Modulation of the gut microbiota facilitates a number of health problems; probiotic feeding with a high-fat diet showed alteration of the gut microbiota composition with a decrease in the gram positive bacteria phyla Firmicutes and Actinobacteria in mice [49]. In contrast, in a mouse model of hyperlipidemia,the probiotic administration of Lactobacillus led to significant changes in the microbiota composition, including