Bacteria. They are many. They are tiny and we cannot see them. They are living on our skin and in our guts and we should be happy that they are with us. Our bodies are walking and talking ecosystems and without them, life would literally be impossible.
They are actually outnumbering our cells by ten and at the same time they are only one-hundredth of the size of a human cell. The majority of bacteria is harmless and heavily needed for our body functions. They are necessary to completely digest food and they are an important part of our immune system. There are numerous functional uses where bacteria are needed like milk and wine production. They are even useful tools for the production of enzymes or medicines and recently discovered to digest ecologically harmful plastic in the oceans.
How and where do they live? Why are some of them good and some of them bad? Why are some of them acting like pathogens and provoke severe diseases? What can we do to tame them and are antibiotics the final answer?