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