In the late 1920s, Scottish scientist Alexander Fleming discovered that a molecule produced by a species of mold could kill many common bacteria. His discovery earned him a Nobel Prize and made him one of the most famous scientists of the 20th century. For the first time doctors had a way to cure infections -- infections that until that time had been completely untreatable.

Personal Story

Alexander Fleming grew up in rural Scotland. The son of a farmer, Fleming later moved to London with one of his brothers and studied medicine at St. Mary's Medical School, where he would later conduct his research. He later served in the Army during the First World War and saw many soldiers die of infections. Fleming wondered whether there was a substance that might be able to treat those infections in the same way that a recently invented drug called salvarsan could treat syphilis.

Accidental Discovery

Fleming's lab was often a mess. One day in 1928, he was sorting through a pile of petri dishes he'd left in a sink when he noticed something unusual. Some mold growing on a field of bacteria in a petri dish had killed all the bacteria around it. Intrigued, Fleming took a sample of the mold and tried growing it on other bacterial cultures. He found the mold was producing a substance that could kill bacteria even in dilute solution.

Further Work

Fleming published his findings but lacked the resources or chemistry know-how to follow up on them. The work of developing penicillin into a drug fell to a couple of Oxford scientists, Howard Florey and Ernst Chain. Florey found Fleming's paper in the back issue of an old journal he was reading one day in 1938, nearly 10 years after Fleming's original discovery. Together with Chain he set out to find a way to isolate penicillin and produce it on a large scale. By 1941 they had succeeded, and penicillin found widespread use during the Second World War.

Fleming's Role

Following his initial discovery, Fleming didn't actually do much follow-up work on penicillin, so the bulk of the development work was actually done by Florey and Chain. The media, however, initially credited Fleming and largely ignored the Oxford group. In 1945 the Nobel Prize all three men shared a Nobel Prize for their work. During Fleming's acceptance speech, he warned that overuse of penicillin might lead to the evolution of resistance. His prediction later proved all too prescient, and many strains of bacteria are resistant to penicillin today.