Our environment is not germ-free: microorganisms have existed on earth for 3.8 billion years. They occur everywhere and make up 70 percent of the living matter (biomass) on our planet. There are 10 to 100 times more microorganisms living on and in every human being than there are cells in the human body.
The human skin and mucous membrane flora as well as the "acid mantle" of skin and mucous membranes formed by bacteria have an important protective function against infections. In the environment, microorganisms also perform essential functions. For example, organic material (from plants or animals) is broken down by microorganisms into its smallest components - sewage treatment plants would not function without them. Finally, bacteria and fungi are also deliberately used in food production, for example in the manufacture of cheese and yoghurt, the maturing of sausages or alcoholic fermentation (wine, beer).
In view of the immense number of types of microorganisms, there are comparatively few germs that can cause diseases. In 2008, infections accounted for 34 percent of all deaths in developing countries. In the industrialised countries, on the other hand, the figure is only around two percent.
Food and germs
Since microorganisms are found everywhere, they are also present in animal husbandry and agriculture: raw milk, even if it has been produced under optimal conditions, contains thousands of bacteria per ml, including a few pathogens. That is why milk should only be drunk after it has been heated. On plants, minor contamination by soil - which contains a large number of microorganisms - can hardly be avoided. Meat always contains small amounts of microorganisms on the surface. Although food is produced to a very high safety standard, it is usually not "absolutely" free of microorganisms, except in sterilised containers such as cans or after irradiation (however, this process is usually not permitted in Europe).