The phenomenon of antibiosis, life prevents life, observed by Goubert and Pasteur in 1877, gave rise to the use of antibiotics in therapy. In fact, on that date has been found that certain microorganisms were sensitive to the action of products produced by other microorganisms. Unfortunately, many of these products were toxic to the cells of higher animals, and only in 1943, the first antibiotic isolated and studied by Sir Alexander Fleming penicillin G – was introduced in clinic. Penicillin was discovered in 1929 when Fleming sought potential antibacterial compounds. He noted that a colony of the fungus Penicillium notatum had grown up on a plate containing the bacterium Staphylococcus aureus and around the fungus had a zone where the bacteria did not grow. The active substance, Fleming called penicillin, but could not isolate it. Several years later, in 1939, Ernst Chain and Howard Florey developed a way to isolate penicillin and used it to treat bacterial infections during the Second World War. The new drug came into use in the clinic in 1946 and had a huge impact on public health. Its discovery and development revolutionized modern medicine and paved the way for the development of many more antibiotics of natural origin.