Answer: Penicillin

Penicillin has been hailed as one of the most significant pharmaceutical discoveries of the 20th century, and rightfully so, as the antibiotic has saved millions of lives the world over since it came into widespread use in the 1940s.

What’s curious about Penicillin is how many times it had been discovered by various researchers over the years and how long it sat after discovery in the 20th century before eventually becoming a widely used medicine. As far back as 1875, researchers like John Tyndall (1875) and Vincenzo Tiberio (1895) of the University of Naples had observed certain molds inhibited bacterial growth, although at the time they had no explanation for the mechanism and, because of poor understanding of disease vectors and transmission, very little energy was invested in studying the phenomenon as a medical tool.

Alexander Fleming is credited as the true discoverer of penicillin as he demonstrated conclusively that if the strain Penicillium rubens was grown in an appropriate substrate, it could be harvested and used as an antibiotic. Although he discovered this in 1928 and was initially quite enthusiastic about the potential medical application, further experiments convinced him that Penicillin wouldn’t last long enough in the human body to actually stave off an infection. He stopped studying it in 1931 only to resume studying it in 1934 and begin searching for a company that could purify and mass produce it.

Although there were several successful trials of Penicillin in the early 1940s, it wasn’t until 1945 that the chemical structure was determined by Dorothy Crowfoot Hodgkin, and then mass produced. Alexander Fleming shared the Nobel Prize in Medicine that year with Ernst Boris Chain, split between the men for their roles in discovering and refining, respectively, what would prove to be a veritable miracle of modern medicine.