الفهرس | Only 14 pages are availabe for public view |
Abstract Probiotics defined as live microorganisms which when administered in adequate amounts confer a health benefit on the host, they are derived from traditional fermented foods, from beneficial commensals, or from human origin. They are the subject of increasing basic and clinical research while also being incorporated into an expanding array of foods, nutritional supplements, and pharmaceutical products (Sazawal et al., 2010). Antibiotics, as substances that either prevent the growth of or kill a living organism, are considered miracle drugs (Prantera and Scribano, 2009). Antibiotics are selective and specific in their targets; thus, these drugs can eradicate invading bacteria without inducing toxicity to the infected host (Guarner et al., 2006). Antibiotics only treat bacterial infections and cannot be effectively used to treat virusrelated infections, such as colds (Costelloe et al., 2010). Probiotics are considered as living drugs that can reduce antibiotic consumption and increase human health development. The consumption of these products is increasing worldwide because probiotics are generally regarded as safe. Anti-carcinogenic, antidiabetic, anti-allergic and anti-inflammatory genetically modified probiotics, as well as oral vaccine development, are counted as new trends of probiotic usage (Bouton et al., 2002). Researchers have documented probiotic effects on various GI and extra-intestinal disorders, such as irritable bowel syndrome (Hoveyda et al., 2009), vaginal infections (Reid et al., 2009), inflammatory bowel disease (Damaskos &Kolios, 2008) and immune enhancement (Gill & Prasad, 2008). Administration of probiotics may pose some danger, although adverse effects seem to be rare. The majority of complications occur in severely immune-compromised subjects or in patients with other life-threatening illnesses managed in intensive-care areas. Although the utilization of probiotics in immune-competent subjects seems to be safe, whether they can be utilized in the prevention of AAD in immune-compromised patients still remains unclear (Botina et al., 2011; Lonnermark et al., 2010). Human gastrointestinal tract is known to host trillions of microbes, the number of which reaches approximately 1014 cells in the entire gut of a healthy individual (Round et al., 2009). Amongst these resident gut microbes, 4000 strains are present constituting the intestinal microbiota (Lan and Zhang, 2017). The complex microbial community of the gastrointestinal tract (GIT) plays an important role in GIT health and in whole body wellbeing by aiding digestion, producing nutrients, protecting against pathogens and in the maturation of the host immune system. A balanced intestinal microbiota and balanced microbe-microbe-host relationships is essential for the performance of all physiological, biochemical and enzymatic machinery in the GIT. Dietary nutrients are converted into metabolites, such as short-chain fatty acids (SCFAs) by the GIT microbiota that serve as biologically active molecules with regulatory functions in the host (Hamer et al., 2008). Gut microbiota has evolved with the host having several functions integrated in the host organism such as metabolic, immune, nutrients absorption, etc….. (Guinane and Cotter, 2013). In 2005 Wang et al., studied diversity of the mucosal biopsies from different locations of the human GIT, jejunum, distal ileum, ascending colon and rectum by sequencing of 347 PCR-amplified 16S rDNA clones finding six phylogenetic phyla of the domain Bacteria: Firmicutes, Bacteroidetes, Proteobacteria, Fusobacteria, Verrucomicrobia, and Actinobacteria. They found Firmicutes and Bacteroidetes phyla accounted for most of the recovered sequences (88 %). At the genera level Prevotella, Streptococcus, Veillonella, Rothia and Haemophilus dominate the healthy human GIT (Nardone and Compare, 2015). Understanding the role and the patterns of modulation of the GIT microbiota may help to normalize the GIT microbial ecosystem and immune system as well as the prevention and/or treatment of enteric infections (Quigley, 2010). Gut microbiota supply the human body with energy from dietary plant polysaccharides producing enzymes, glycoside hydrolases, poly-saccharidelyases and carbohydrate esterases, which are absent in the human genome. Gut microbiota may adjust to metabolize and get energy from dietary components (Hehemann et al., 2010). A major function of the microbiota is protection against colonization by pathogens and over growth of potentially harmful indigenous microorganisms that can result from the disruption in the harmony in the microbial community. The mechanisms that regulate the ability of the microbiota to restrain pathogen growth are complex and include competitive metabolic interactions; localization to intestinal niches and induction of host immune responses. Pathogens, in turn, have evolved strategies to escape from commensal-mediated resistance to colonization (Kamada et al., 2013). Incorporation of probiotic bacteria has an ability to become stable the immunological barrier in the gut mucosa by declining the generation of local pro-inflammatory cytokines. Probiotics is used for treatment of the inflammatory bowel disease, such as ulcerative colitis, crohn‘s disease, and pouchitis (Shyamala et al., 2016). GIT microbiota, particularly certain organisms have adapted to the GIT niche, over the course of evolution, having different functions like nourishment of the host or training the immune system. With a better understanding of the microorganisms in the GIT, the manipulation of the GIT microbiota might prove to be a future targeted therapy for a number of conditions. Although probiotics and prebiotics are being applied and some treatments are well established, a lot of effort is still required in order to a better understanding and characterization of the microbiota and the microbe-microbe-host relationships to achieve an effective therapy (Calo-Mata et al., 2016). Probiotics can be useful in treating hepatic diseases due to their potential ability to modulate alterations in the gut microbiota, intestinal permeability, and immune and inflammatory responses. Extensive evidence in murine and in-vitro models shows the role of probiotics in several liver diseases, specifically in certain functional properties such adhesion and pro-inflammatory response (Senaka et al., 2014). The pathogenic mechanism involved in liver damage secondary to alcohol abuse is endotoxemia. There are structural and functional changes in the liver and intestine which explain the increased intestinal permeability or liver sensitivity. Experimental data using L. plantarum encapsulated alginate beads induce a dose-dependent reduction of endotoxin level in rats exposed to alcohol. Also a reduction in liver function test was observed, as well as molecular markers of inflammation (e.g. TNF-α and IL-12), Similar results are observed with VSL#3, and interestingly the results were similar if VSL#3 was enriched with glutamine or if it was in a heat-killed form. (Murguia et al., 2013). Patients assigned to a low calorie diet with fat and carbohydrate restrictions for 1 year showed modifications of their gut microbiota composition, with fewer irmicutes and more Bacteroidetes, along with weight-loss. These findings suggest that Firmicutes spp. possess more diverse enzymes capable of digesting and extracting calories from complex polysaccharides (Chen et al., 2013). The gut–liver axis plays a central role in the pathogenesis of this disease. Disturbance of the microbiota, in particular small intestinal bacterial overgrowth, occurs in 20–75% of patients with chronic liver disease, especially in NAFLD patients, and is associated with the severity of steatosis (Aller et al., 2011). Most of the studies performed in animal models and humans have shown that probiotics reduce pro inflammatory cytokines and liver enzymes, and have confirmed the benefits of different strains of probiotics in the treatment of NASH/NAFLD. The evidence in animal models is clear, but more human studies with larger sample sizes are needed to be able to recommend the use of probiotics in all patients with liver disease. Recent meta-analysis demonstrates the improvement in liver function test and inflammatory marker in patients with NAFLD suggesting a real hypothesis about the clinical use of probiotics in this condition (Ma et al., 2013). |