الفهرس 
Compositional Diversity of the Gut BacteriaOnly 14 pages are availabe for public view
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Abstract
It is known for over three decades that the human body contains tenfold more microbial cells (1014) than human cells. These microorganisms colonise practically every surface of the human body that is exposed to the external environment, including the skin, oral cavity, respiratory, urogenital and gastrointestinal tract. Of these body sites, the gastrointestinal (GI) tract is by far the most densely colonised organ. The complex community of microorganisms residing in or passing through the GI tract is referred to as gut bacteria.
The gut bacteria plays a role in metabolic, nutritional, physiological and immunological processes in the human body. It exerts important metabolic activities by extracting energy from otherwise indigestible dietary polysaccharides such as resistant starch and dietary fibres. These metabolic activities also lead to the production of important nutrients, such as short-chain fatty acids (SCFA), vitamins (e.g. vitamin K, vitamin B12 and folic acid) and amino acids, which humans are unable to produce themselves.
In addition, the gut bacteria participates have a continuous and dynamic effect on the host’s gut and systemic immune systems. The bacteria are key in promoting the early development of the gut’s mucosal immune system both in terms of its physical components and function and continue to play a role later in life in its operation. The bacteria stimulate the lymphoid tissue associated with the gut mucosa to produce antibodies to pathogens. Furthermore, gut bacteria is involved in the development, maturation and maintenance of the GI sensory and motoric functions, implicated in preventing allergies.
On the other side, bacteria in the digestive tract have pathogenic properties in addition to their health-inducing ones: they can produce toxins, carcinogens and have been implicated in such conditions as multisystem organ failure, sepsis, colon cancer, peptic ulcer and inflammatory bowel disease (IBD).
Gut bacteria have important role in the development of obesity, insulin resistance and diabetes in the host through several mechanisms: increased energy harvest from the diet, altered fatty acid metabolism and composition in adipose tissue and liver.
A major factor in health is the balance of bacterial numbers; if the numbers grow too high or low, it will result in harm to the host. The host has enzymes to regulate this balance.
Altering the numbers of gut bacteria, for example by taking broad-spectrum antibiotics may affect the host’s health and ability to digest food. Antibiotics can cause ”antibiotic-associated” diarrhea (AAD) by irritating the bowel directly, changing the levels of gut flora, or allowing pathogenic bacteria to grow. Changing the numbers and species of gut flora can reduce the body’s ability to ferment carbohydrates and metabolize bile acids and may cause diarrhea and indigestion.
Finally, an overview is presented of ways to modulate gut bacteria with specific attention for the use of probiotics, defined as live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.
Probiotics have role in intestinal barrier function.It stimulate mucin production, and therefore enhance the self protecting properties of intestinal epithelium. In addition, it have also been used in prevent post operative infections in patients undergoing abdominal surgery (biliary cancer, liver transplantation and pancreaticoduodenectomy.
Probiotics have important role in liver health.Its action most relavant to liver disease are modification of intestinal barrier function and prevention of bacterial translocation which aid in treatment hepatic encephalopathy, non alcoholic fatty liver and liver cirrohsis.