the human adult microflora is colon

the human adult microflora is colonized by approximately
10^14 microbial cell, about 10 times more than all tissue cells
of the body. this high metabolic rate suggests important
regulatory effects on body functions, especially in the colon
where the greatest concentration of up to 5x10^11 bacterial cell
per g is found. the human microbiota is stable at different
anatomic locations along the gut, but absolute numbers vary
greatly, ranging from 10^11 cells/g content in the ascending
colon to 10^7 in the distal ileum and 10^3 in the proximal
ileum and jejunum. anaerobes are more abundant that aerobes
in the bacterial community and a majority of the population are
representatives of two divisions: the Bacteroidetes and
Firmicutes. at birth the gut is sterile and is colonized
immediately, although there are marked variations in microbial
composition between individuals. More than 400 species are
included: Gram-positive, anaerobic genera Bacteroides,
eubacterium, Bifidobacterium, Peptostreptococcum,
streptococcum, lactobacillus, Fusobacterium, ruminococcus,
clostridium and escherichia. some of these bacteria are
potential pathogens and can be a source of infection and sepsis
under some circumstances, when the integrity of the bowel
barrier is physically or functionally breached. these bacteria
maintain the integrity of gut mucosa and the production of short
chain fatty acids (scFa) in a favorite ratio . the
enormous numbers and diversity of microorganisms in the
human intestine contribute to a diverse set of functions, which
complement the host for important features such as digestion of
complex carbohydrates. the interaction between animal and
bacterial cells is very important in the human gastrointestinal
tract. the bacterial microbiota has established multiple
mechanisms to influence the human host in a beneficial fashion
and maintain their stable niche. the human host coevolved with
a normal microbiota developed and optimized immune
mechanisms. Both the impact of gut microbiota on disease and
the impact of disease on gut microbiota need to be investigated
to establish a good treatment in the gastrointestinal disease. the
gut microflora exerts a considerable influence on host
biochemistry including enzymatic activity of intestinal
contents, oxidation-reduction potential of luminal contents,
short chain fatty acid production in the lumen, host physiology,
host immunology, modification of host-synthesized . several
studies showed a decrease in Bifidobacteria and an increase in
clostridia, lactobacilli, streptococci and enterobacteriaceae in
the gastrointestinal tract of elderly people (5-8). the genera
Bifidobacterium are the dominant probiotic bacteria inhabiting
the distal jejunum ileum and large intestine of humans and
other warm-blooded animals. Bifidobacterium spp has many
beneficial effects on human health, including:
immunomodulation, reducing serum cholesterol, promoting
lactose digestion and protecting against colon cancer. changes
in the microflora could alter the metabolic environment of the
colon with important modifications in the concentration of
healthy substances that may alter the motor and secretor
functions of the bowel. so, changes in the microflora increase
susceptibility to gastrointestinal functional disorders, infections,
inflammation or cancer. conversely, probiotics can promote the
homeostasis of the colonic microbiota. recent studies have
suggested that the gut microbiota may have a role in
gastrointestinal diseases through the regulation of energy
metabolism by several mechanisms (that is, energy harvest
from the diet, regulation of fat storage, modulation of afferent
gastrointestinal peptide hormones, induction of metabolic
endotoxemia)