What is the intestinal flora?
The intestinal flora is the totality of all intestinal bacteria that colonize parts of the human colon (in small quantities also the rectum). The term intestinal flora goes back to the earlier assumption that this collection of microorganisms belongs to the plant kingdom (flora = plant world). However, since the bacteria belong to a separate kingdom (protista), the term intestinal bacteria, intestinal microbiome, or intestinal microbiota is a better term.
The majority of the intestinal flora – 500 to 1000 different intestinal bacterial species – live in the colon (on the intestinal wall). Their number is estimated at about 10 trillion, their total weight at about one and a half kilograms.
Intestinal flora: enterotypes
Depending on the dominant bacterial strain, three different types of intestinal flora can be roughly distinguished, so-called enterotypes (from Latin entero = intestine):
- Enterotype 1: contains a particularly large number of bacteria of the genus Bacteroides, which break down carbohydrates and are good producers of the vitamins biotin, riboflavin and pantothenic acid.
- Enterotype 3: contains particularly large numbers of Ruminococcus bacteria, which are very good at digesting sugars and proteins
Experts discuss whether the composition of the intestinal flora can be specifically and permanently influenced by the type of diet (fiber content, etc.).
Development of the intestinal flora in children
The intestine of a child in the womb is still completely sterile. It is not until the birth process that its colonization with microorganisms begins: Bacteria of the maternal intestinal flora enter the baby’s gastrointestinal tract via the baby’s mouth during a natural (vaginal) birth, where they build up the child’s intestinal flora and gradually form a stable microbiome.
What is the function of the intestinal flora?
The vital intestinal flora fulfills various tasks:
Food digestion: the intestinal bacteria support digestion. They produce short-chain fatty acids such as butyrate, acetate and propionate from indigestible dietary fiber. These meet a large part of the energy requirements of the mucous membrane of the large intestine. In addition, the short-chain fatty acids promote the intestinal muscles and play an important role in the motility of the intestines (intestinal motility).
Neutralizing toxins: Some gut bacteria can neutralize toxic (poisonous) substances, such as nitrosamines and polycyclic aromatic hydrogens. Many of these compounds are considered carcinogenic.
Activating drugs: Some drugs are only converted to their active (effective) form in the course of metabolism by the intestinal flora. This applies, for example, to antibiotics from the sulfonamide group and to the anti-inflammatory agent sulfsalazine.
Immune defense: The intestinal flora is extremely important for immune defense. The intestinal mucosa has a surface area of 300 to 500 square meters and thus represents the largest boundary surface of the body. The “good” intestinal bacteria that settle here prevent pathogenic germs from spreading and causing intestinal infections. In addition, the intestinal bacteria train the part of the immune system localized in the intestine (intestine-associated immune system) via special signal structures.
Where is the intestinal flora located?
The intestinal flora mainly colonizes the large intestine (colon). In small amounts, intestinal bacteria are also found in the rectum.
What problems can the intestinal flora cause?
The colonization of the small intestine with intestinal bacteria is low. This is to prevent nutrients from food such as vitamin B12 from being metabolized by intestinal bacteria instead of being absorbed into the body via the mucosa of the small intestine. However, if surgical procedures result in blind-ended intestinal loops, for example, the bacterial density in the small intestine can increase to such an extent that the resulting vitamin B12 deficiency causes anemia.
If the secretion of gastric acid is inhibited by medication (for example, in the case of heartburn or gastritis), this can disrupt the composition of the intestinal flora over time.
The administration of antibiotics can also disrupt the human microbiome: Individual intestinal bacterial species can be inhibited in their growth and others can be promoted in their growth – the balance of the intestinal flora is lost. The result can be mild symptoms such as diarrhea, but also severe inflammation in the colon.
If the Bifidus and Bacteroides intestinal bacteria that synthesize vitamin K, which is important for blood clotting, are damaged by drugs, blood clotting may be disrupted.
The composition of the intestinal flora influences the occurrence of colon cancer and other diseases.
Keyword probiotics
With probiotics, many people specifically take “good” bacteria for the intestines (such as lactic acid bacteria) to strengthen their intestinal flora, for example in the case of diarrhea. When taken in high enough amounts, probiotics can actually prevent diarrhea caused by rotavirus, as well as help with diarrhea caused by radiation therapy or antibiotics.
However, the bacteria supplied as probiotics only settle in the intestinal flora if taken regularly. If the intake is stopped, they disappear again and the “old” intestinal flora re-establishes itself over time.
