Monthly Archives: February 2015

Microflora of the gastrointestinal tract: a review.

·
Methods Mol Biol. 2004;268:491-502.

Microflora of the gastrointestinal tract: a review.

Hao WL1, Lee YK.

Author information

Abstract

The mucosal surface of the human gastrointestinal (GI) tract is about 200-300 m2 and is colonized by 1013-14 bacteria of 400 different species and subspecies. Savage has defined and categorized the gastrointestinal microflora into two types, autochthonous flora (indigenous flora) and allochthonous flora (transient flora). Autochthonous microorganisms colonize particular habitats, i.e., physical spaces in the GI tract, whereas allochthonous microorganisms cannot colonize particular habitats except under abnormal conditions. Most pathogens are allochthonous microorganisms; nevertheless, some pathogens can be autochthonous to the ecosystem and normally live in harmony with the host, except when the system is disturbed. The prevalence of bacteria in different parts of the GI tract appears to be dependent on several factors, such as pH, peristalsis, redox potential, bacterial adhesion, bacterial cooperation, mucin secretion, nutrient availability, diet, and bacterial antagonism. Because of the low pH of the stomach and the relatively swift peristalsis through the stomach and the small bowel, the stomach and the upper two-thirds of the small intestine (duodenum and jejunum) contain only low numbers of microorganisms, which range from 103 to 104 bacteria/mL of the gastric or intestinal contents, mainly acid-tolerant lactobacilli and streptococci. In the distal small intestine (ileum), the microflora begin to resemble those of the colon, with around 107-108 bacteria/mL of the intestinal contents. With decreased peristalsis, acidity, and lower oxidation-reduction potentials, the ileum maintains a more diverse microflora and a higher bacterial population. Probably because of slow intestinal motility and very low oxidation-reduction potentials, the colon is the primary site of microbial colonization in humans. The colon harbors tremendous numbers and species of bacteria. However, 99.9% of colonic microflora are obligate anaerobes.

PMID:

 

15156063

 

[PubMed – indexed for MEDLINE]

How Microbes Keep Us Healthy [Infographic]

·

The gut houses trillions of microbes. They eat what you eat. Many specialize in fermenting the soluble fiber in legumes, grains, fruits and vegetables. Certain microbial species are adept at colonizing the mucous layer of the gut. Mucus contains antimicrobial substances that keep the microbiota at a slight distance. But it also contains sugars such as those found in breast milk. Some microbes, often the same ones that specialize in fermenting fiber, can use these sugars as sustenance when other food is not available. The by-products of fiber fermentation nourish cells lining the colon. Some by-products pass into the circulation and may calibrate our immune system in a way that prevents inflammatory disorders such as asthma and Crohn’s disease.

healthy2

 

Among Trillions of Microbes in the Gut, a Few Are Special

·

Amid the trillions of microbes that live in the intestines, scientists have found a few species that seem to play a key role in keeping us healthy.

In the mid-2000s Harry Sokol, a gastroenterologist at Saint Antoine Hospital in Paris, was surprised by what he found when he ran some laboratory tests on tissue samples from his patients with Crohn’s disease, a chronic inflammatory disorder of the gut. The exact cause of inflammatory bowel disease remains a mystery. Some have argued that it results from a hidden infection; others suspect a proliferation of certain bacteria among the trillions of microbes that inhabit the human gut. But when Sokol did a comparative DNA analysis of diseased sections of intestine surgically removed from the patients, he observed a relative depletion of just one common bacterium, Faecalibacterium prausnitzii. Rather than “bad” microbes prompting disease, he wondered, could a single “good” microbe prevent disease?

See complete article.

How Gut Bacteria Help Make Us Fat and Thin

·
Intestinal bacteria may help determine whether we are lean or obese
Jun 1, 2014 |By Claudia Wallis
Rafa Alvarez

For the 35 percent of American adults who do daily battle with obesity, the main causes of their condition are all too familiar: an unhealthy diet, a sedentary lifestyle and perhaps some unlucky genes. In recent years, however, researchers have become increasingly convinced that important hidden players literally lurk in human bowels: billions on billions of gut microbes.Throughout our evolutionary history, the microscopic denizens of our intestines have helped us break down tough plant fibers in exchange for the privilege of living in such a nutritious broth. Yet their roles appear to extend beyond digestion. New evidence indicates that gut bacteria alter the way we store fat, how we balance levels of glucose in the blood, and how we respond to hormones that make us feel hungry or full. The wrong mix of microbes, it seems, can help set the stage for obesity and diabetes from the moment of birth.

http://www.scientificamerican.com/article/how-gut-bacteria-help-make-us-fat-and-thin/