In 1928, a chance event in Alexander Flemings’s London laboratory quite literally changed the course of medicine. While studying influenza, specifically the staphylococcal bacteria, Fleming noticed that mold had developed on a set of culture dishes which were uncovered and near a window. These mold cultures had a bacteria free circle around them. This had never been seen before as he realised the bacteria near the mold were dying. Fleming discovered that it wasn't the mold itself that had destroyed the bacteria but the 'juice' that it had produced. The 'mold juice' was what he called Penicillin.
Fleming struggled to isolate a pure Penicillin due to it being very unstable. For a while after, the medical community was not very enthusiastic about his discovery, especially as he was unable to isolate it in bulk. In 1940, two fellow scientists Ernest Chain and Howard Florey, became interested in Penicillin and soon were able to mass produce it for use during World War 2. As a result, Fleming received many awards for his discovery, including the Nobel Prize in Medicine and Physiology in 1945.