Bacteria in the intestine

Introduction

The human body is a habitat for over 1012 species of bacteria, a large proportion of which populate the intestine. Bacteria are generally associated with infections and diseases. In the intestine, however, bacteria have an important function in maintaining the immune system and protecting against harmful microorganisms. For this reason, a healthy intestinal flora is important for health.

The natural intestinal flora

The first bacteria of the natural intestinal flora are transmitted with the contact between the newborn and its mother during birth. The bacteria of the mother’s vaginal flora and perianal flora (bacterial colonisation around the anus) reach the baby’s digestive tract via the mouth. A large part of these bacteria make up the later normal intestinal flora (e.g. E. coli, enterobacteria & streptococci).

Bacteria are then absorbed through food during childhood. The healthy intestinal flora of an adult consists mainly of anaerobic (without oxygen living) bacteria. The number is about 10-100 billion bacteria in the human digestive tract.

A large part of these is located in the large intestine. It is currently estimated that there are about 1800 genera and 36000 different types of bacteria. The function of the bacteria in the intestine is, among other things, to produce short-chain fatty acids, stimulate intestinal peristalsis (movement of food through the intestinal muscles), support digestion and strengthen the immune system.

The most important factor in the development of natural bacteria in the intestine is nutrition. A high consumption of convenience food in the form of fast food or frozen food is not recommended. The preservation methods of the food keep the food as germ-free as possible, but this also kills the benign bacteria that would settle in the intestine.

Sour milk products such as quark, yoghurt or cheese are also recommended, which have a beneficial effect on the acid flora of the intestine due to their acidic character. Hardened fats and overheated fats should be avoided. The overheated fats occur in pan-fried dishes, the nutrients can be used well by the defective intestinal flora.

Alternatively, the build-up of the intestinal flora can be achieved by substitution (replacement) of “good” bacteria. A substitution of E. coli is not possible, as a settlement of the bacteria depends on various factors. With lactobacilli and bifidobacteria, however, a substitution therapy is possible and is used more frequently.

Species of bacteria

The colonization of the intestine with bacteria begins in naturally born children already during the vaginal delivery. The first strains of bacteria can be detected shortly after birth. Especially the colonization of the intestine with Escherichia coli, Enterobacteriaceae and Streptococci starts quite early.

Since the natural birth process plays a decisive role in the bacterial colonization of the intestine, the early childhood intestinal flora can be significantly altered by a birth by Caesarean section. Children born by Caesarean section initially show an unnaturally changed intestinal flora that corresponds to the maternal skin flora. In addition to the birth process, nutrition also has a considerable influence on which bacteria settle in the intestine.

In this context, it is usually possible to draw conclusions from the intestinal flora as to whether a child is being breastfed or is merely receiving bottle feeds. In the case of fully breastfed children, lactic acid-producing bacteria (so-called bifidobacteria and lactobacilli) can be found in both the large and small intestine within the first weeks of life. The lactic acid (lactate) produced by these bacteria strains causes a drop in the pH value inside the intestine.

The intestinal environment of these children therefore takes on an acidic character. On the other hand, children who are mainly fed bottle-fed foods develop bacteria in the intestines at an early age that correspond to the adult intestinal flora. In adulthood, the intestinal flora is characterised by a large number of different species of bacteria.

In healthy adults, so-called anaerobic bacteria (bacteria that do not require oxygen to survive) can be detected in the intestine. About 90 percent of the bacteria in the area of the adult colon can be assigned to the genera Firmicutes, Bacteroidetes, Proteobacteria and Actinobacteria. In contrast, the microflora of the small intestine mainly contains facultatively anaerobic bacteria of the genera Enterococcus and Lactobacillus.

Facultatively anaerobic bacteria can survive in both oxygen-poor and oxygen-rich environments. In addition to these health-promoting bacteria, the intestine can also be a colony of pathogenic bacterial pathogens. Classical examples of such bacteria in the intestine are enterohaemorrhagic E. coli (EHEC), enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC) and enterotoxic E. coli (ETEC).

Bacteria from the group of enterohaemorrhagic E. coli (EHEC) cause bloody (haemorrhagic) diarrhoea in humans. E. coli (Escherichia coli) is a bacterium that occurs in our intestines. Most strains of the genus E. coli are not pathogenic for humans.

It is rather an important part of the intestinal flora. E. coli plays an important role in digestion – the bacterium is a major producer of vitamins. Especially vitamin K is produced by E. coli.

However, the strains, which are pathogenic (disease-causing), can cause urinary tract infections (UPEC), meningitis (NMEC) or intestinal diseases (EHEC/AIEC). However, these pathogenic strains do not normally occur in our intestines. In order to trigger a urinary tract infection, the bacteria must also first come into contact with the urinary tract.