الفهرس 
IntroductionOnly 14 pages are availabe for public view
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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).