The term can be defined as follows: A microorganism is an organism that requires a microscope to observe. However, there are a few exceptions: giant organisms such as special bacteria or single-celled eukaryotes as well as micro-algae that can be seen with the naked eye 1 .
Microorganisms are divided into different groups: bacteria, viruses, fungi, archaea, microalgae and protozoa. This article focuses on the first three because they are of greater importance to the human organism:
Bacteria are single-celled organisms, meaning that they only consist of a single cell. In contrast to humans and animals, they belong to the prokaryotic organisms whose cells do not have a nucleus. Their size is between 1 and 10 micrometers.
Viruses are not living organisms because they cannot carry out their own metabolism. They need the organelles of a host cell to reproduce. A virus is actually not a cell, but rather just a capsule with genetic information. Their size is between 0.01 and 0.1 micrometers, making them about 100 times smaller than bacteria.
Fungi are eukaryotes, which means, among other things, that their cells have a nucleus. They are usually multicellular and consist of fungal threads (hyphae). These form a mycelium, another word for it is mushroom plexus. The threads cannot be seen with the naked eye; only the braid can be seen by us humans without a microscope. Fungi either feed on dead organic material, live through symbiotic exchange or through parasitic colonization of plant or animal host cells 2 .
Beneficial insects and pests – our microbiome
It quickly becomes clear that fungi and bacteria in particular have beneficial but also damaging effects on the human organism. We consist of approximately 30 trillion body cells; If you add the cells of all the microorganisms that live on and in us, you get about 39 trillion 4 . Our metabolism depends on the microorganisms that colonize us and vice versa.
It is a so-called symbiosis. The term describes the coexistence of living beings of different species for mutual benefit, so to speak a win-win situation. The human microbiome influences our immune system, metabolism and endocrine system 3 . In humans, the digestive tract, skin, nose and vagina are colonized by microorganisms. Only the areas of the brain, lungs, abdominal cavity, bladder and blood are sterile 11 .
Classification of different microorganisms
Strictly speaking, the term microbiome includes not only the symbiotic microorganisms, but also the commensal, opportunistic and pathogenic ones. In this context, commensal means that they can be classified as neither pathogenic nor health-promoting. They are simply there, almost as neutral as Switzerland. The pathogenic invisible residents are ultimately the ones who harm us; they are pathogens. Opportunistic microorganisms are something in between, as they are neutral most of the time, but can develop into pathogenic ones when they grow rapidly from a specific number 4 . It is therefore obvious that we want to preserve the commensal microorganisms as much as possible and keep the number of opportunistic ones small so that no pathogenic ones arise.
The skin flora
Our skin is a complex organ that serves as a mechanical and chemical barrier to the environment. It also plays an important role as a sensory organ and in communication: we can perceive temperatures, pain or pleasant touches through the skin; it turns red when we are embarrassed and pale when we feel unwell. It also regulates body temperature, produces vitamin D with the help of sunlight and is of great importance in immune defense 5 :
There are a large number of microorganisms on the surface of the skin, including bacteria, fungi and mites. The skin flora refers to the entirety of these microorganisms that are not pathogenic for our body 6 . On the one hand, these include non-pathogenic ones, which play an important role in our health: They protect the body from pathogens by preventing pathogenic germs from entering the system.
On the other hand, the commensal microorganisms described above can also be found on the skin. However, these can mutate into pathogenic ones if the immune system is weakened or if the skin is injured. There is also a protective acid mantle on the skin; the PH value is between 5.4 and 5.9. This is an optimal living condition for the non-pathogenic species that live there. However, the pathogenic ones are primarily inhibited in their growth.
In addition, the health-preserving microorganisms destroy the harmful ones. So if the former are in the majority, it is a win-win situation 10 . It is therefore obvious that the healthy skin flora is promoted if its natural PH value is maintained and it is not exposed to injuries if possible. Washing your hands too often or using products that change the pH value of your skin should be avoided.
If the skin is not intact, pathogenic germs can enter the organism through it. Conversely, it is also possible that pollutants that have entered the body via other routes need to be detoxified through the skin. This then becomes visible on the surface of the skin.
The diversity of bacterial species on the skin is enormous and varies greatly depending on the location. Moist areas such as the armpits or anal folds have different inhabitants than, for example, dry forearms. The bacteria feed on scales, sebum and sweat and their metabolic breakdown products ultimately form our individual body odor 11 .
The surface in the mouth is essentially a continuation of the outer skin, except that it is a mucous membrane that must be moist. There are over 700 species of bacteria and fungi here, including mainly commensal and opportunistic but also pathogenic ones 11 .
The microorganisms in the mouth form a so-called biofilm. This is a mucous coating on our teeth that arises in which the microorganisms adhere together with proteins, polysaccharides and electrolytes to form a complex structure. This is the only way they can hold on to such a smooth surface 4 .
The coating contains all three forms of bacteria described in the first section. Some of the bacteria benefit our health and in return benefit from our oral cavity as a habitat. This relationship is called mutualism. In the first years of life, these microorganisms are involved in the maturation of our immune system. They also keep potential pathogens away, because when they have the upper hand, pathogenic bacteria are unable to spread further. An imbalance in this ecosystem can lead to diseases:
Tooth decay is a typical example of this. The disease occurs when the bacterial composition changes in such a way that the opportunistic germs change into pathogenic ones and gain the upper hand. According to the latest scientific findings, the main cause of diseases in the oral cavity is not the lack of brushing, but rather an imbalance in the ecological system.
It was also found that there are enough people who practice meticulous oral hygiene but still get tooth decay. This is caused by acid-producing pests that keep the pH value in saliva and within the biofilm permanently too low 4 . Ideally, the saliva should be slightly alkaline; a pH value of and above 7 provides a good basis for healthy oral flora.
Above all, an incorrect diet, which promotes the proliferation of pathogens, is the cause of hyperacidity in the mouth. Sugar plays a crucial role here: the pathogenic bacterium Streptococcus Mutans, which is normally found in a safe population size in the biofilm, feeds on sugar. If there is enough sugar, it can multiply quickly and releases acids as a metabolic product that can normally neutralize the complex ecosystem in the mouth. However, if you constantly consume sugar, at some point it will no longer be able to regenerate itself and the acids will attack the minerals in the teeth, destroy the tooth enamel and ultimately lead to lesions in the tooth 14 .
How can you maintain the health of your oral flora?
From the findings in the last section, it can be concluded that sugar should be consumed sparingly in the diet. Hidden sugars in convenience foods, milk as well as fruits and juices should not be ignored. Sufficient fluid intake is also necessary because when the mouth is dry, there is less saliva and this is a basic requirement for the balance of the local ecosystem. Good fats such as olive oil, coconut oil and aloe vera also contribute to this balance. They nourish the pellicle, the protective shield of our teeth. You can imagine it as a fine retina that constantly re-forms if, for example, it is destroyed while eating. It protects the tooth from abrasion during chewing and from acids 4 .
Before food enters the intestines, where 99% of the bacteria that colonize us are located, it is stored in the stomach and broken down into a pulp. In contrast to the alkaline oral flora, it is acidic; the pH value of stomach acid is between 1 and 1.5. This environment is optimal for breaking down proteins and destroying bacteria 12 . In fact, the pathogenic bacterium Helicobacter pylori was discovered in 1979, which can only carry out its metabolism in the human stomach. Previously, science assumed that no microorganisms could survive this acidic atmosphere. Helicobacter is responsible for stomach cancer; Since this discovery, cases of the disease in the United States have decreased by 80% 11 .
The food is released bit by bit from the stomach into the small intestine, where relatively few microorganisms reside. After macronutrients and micronutrients have been released into the human blood via the intestinal villi, indigestible carbohydrates (fiber), water, electrolytes and waste products are further released into the large intestine.
In the intestine, especially in the large intestine, there is a high number of microorganisms that perform many important tasks for us: They produce various B vitamins such as vitamin K2, are involved in sugar absorption, supply the intestinal mucosa with nutrients and produce short-chain fatty acids. They also stimulate intestinal peristalsis, which causes the food to move, and help break down food components and their indigestible food fibers.
In order for the useful intestinal inhabitants to be able to do their jobs for us, they have to receive the right food: Carbohydrates that are indigestible for our intestines in particular keep the intestinal bacteria alive. These are also known under the colloquial name fiber. The scientific term prebiotics is a bit broader and means non-digestible food components that serve as food for the microorganisms in our digestive tract 11 .
Vegetables and fruits contain fiber, but also grains, seeds and nuts. The intestinal inhabitants particularly like chicory, salsify, Jerusalem artichoke, yacon, psyllium husks and fermented foods.
Body fat storage and health depend on a healthy microbiome
Researchers have found that various bacteria have an influence on our body weight. An overpopulation of the Fimicutes tribes could clearly be seen in overweight people. This condition appears to cause more carbohydrates to be digested and absorbed than usual. The opponents of the Firmicutes are the Bacteroidetes, which are associated with reduced body fat storage.
Optimally, both strains are present in a 1:1 ratio; If this relationship gets out of balance, more or less sugar from actually indigestible carbohydrates can be absorbed, converted into body fat and stored 7 . For people who eat little but cannot lose weight, an analysis of the microbiome makes sense. In addition, these people can try to eat low-carbohydrate for a while, and success is often already achieved.
Since, as already mentioned, the intestinal bacteria are involved in the production of fat cells in a healthy intestinal mucosa, their relevance to our health is obvious: our intestinal mucosa must be intact so that only what is good for us gets into our system. If the surface of the intestine is damaged, substances enter the bloodstream and tissue that harm us and lead to inflammation.
Our body is a complex, ecological system. It cannot be considered as a being consisting only of human body cells. Rather, it is a symbiosis between microorganisms and the human organism. Our health depends on the microorganisms being present in a healthy balance. To do this, we must, above all, eat correctly. An important factor is to use sugar very sparingly and to consume lots of vegetables and enough fluids in the form of water.
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