English

Noun

1. Microscopic plant life, especially the bacterial colonies found in the gut of normal, healthy animals and humans.

Related terms

• microbiota
• microfauna

The gut flora are the microorganisms that normally live in the digestive tract and can perform a number of useful functions for their hosts. Though widely known as the "intestinal microflora", this is technically a misnomer since the word root "flora" pertains to plants and biota refers to microbial life such as bacteria other than plants. Thus the more appropriate term "intestinal microbiota" is coming into use, though its use has not eclipsed the entrenched use and recognition of "flora" with regard to intestinal bacteria, and for the time being, both terms are being used in different textbooks.

The average human body, consisting of about 1013 (10,000,000,000,000 or about ten trillion) cells, has about ten times that number of microorganisms in the gut.

Bacteria make up most of the flora in the colon and 60% of the mass of feces. Fungi and protozoa also make up a part of the gut flora, but little is known about their activities.

Research suggests that the relationship between gut flora and humans is not merely commensal (a non-harmful coexistence), but rather is a mutualistic, symbiotic relationship. The first part of the colon is mostly responsible for fermenting carbohydrates, but in the cecum aerobic bacteria reach high densities. so DNA isolation and identification is difficult. Populations of species vary widely among different individuals but stay fairly constant within an individual over time. Infants born by caesarean section may also be exposed to their mothers’ microflora, but the main exposure is from the surroundings. After birth, environmental, oral and cutaneous bacteria are readily transferred from the mother to the infant through suckling, kissing, and caressing. All infants are initially colonized by large numbers of E. coli and streptococci. Within a few days, bacterial numbers reach 108 to 1010 per gram of feces. During the first week of life, these bacteria create a reducing environment favorable for the subsequent bacterial succession of strict anaerobic species mainly belonging to the genera Bifidobacterium, Bacteroides, Clostridium, and Ruminococcus. Breast-fed babies become dominated by bifidobacteria, possibly due to the contents of bifidobacterial growth factors in breast milk. In contrast, the microflora of formula-fed infants is more diverse with high numbers of Enterobacteriaceae, enterococci, bifidobacteria, Bacteroides, and clostridia. After the introduction of solid food and weaning, the microflora of breast-fed infants becomes similar to that of formula-fed infants. By the second year of life the fecal microflora resembles that of adults.

Functions

Bacteria in the gut fulfills a host of useful functions for humans, including digestion of unutilized energy substrates; stimulating cell growth; repressing the growth of harmful microorganisms; training the immune system to respond only to pathogens; and defending against some diseases.

Carbohydrate fermentation and absorption

Without gut flora, the human body would be unable to utilize some of the undigested carbohydrates it consumes, because some types of gut flora have enzymes that human cells lack for breaking down certain polysaccharides.

Some species of gut flora, such as some of those in the Bacteroides genus, are able to change their surface receptors to mimic those of host cells in order to evade immune response. Bacteria with neutral and harmful effects on the host can also use these types of strategies. The host immune system has also adapted to this activity, preventing overgrowth of harmful species. The incidence and prevalence of IBD is high in industrialized countries with a high standard of living and low in less economically developed countries, having increased in developed countries throughout the twentieth century. The disease is also linked to good hygiene in youth; lack of breastfeeding; and consumption of large amounts of sucrose and animal fat. People may take the drugs to cure bacterial illnesses or may unintentionally consume significant amounts of antibiotics by eating the meat of animals to which they were fed.

Probiotics & Prebiotics

Since the lack of gut flora can have such harmful health effects, the use of probiotics has anti-inflammatory effects in the gut and may be useful for improving health. Prebiotics are dietary components that can help foster the growth of microorganisms in the gut, which may lead to better health. can occur in a number of different diseases.

If the gut is perforated, bacteria can invade the body, causing a potentially fatal infection. Aerobic bacteria can make infection by anaerobes worse by using up all available oxygen and creating an environment favorable to anaerobes.

It has been noted that though Ulcerative Colitis and Crohn's disease (two types of IBD) probably have genetic components, they are not inherited in a Mendelian fashion and are thus probably due to a complex set of factors rather than solely to a gene. However, while some bacterial strains such as C. difficile

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