Sir Alexander Fleming (1881-1955), British bacteriologist and Nobel laureate, best known for his discovery of penicillin. Born in Lochfield, Ayr (now part of Strathclyde), Scotland, Fleming had a brief military career before a small legacy enabled him to begin studying medicine in 1901 at St Mary’s Hospital Medical School of the University of London. He remained associated with St Mary’s throughout his career, ending as Director of what (from 1948) was called the Wright-Fleming Institute of Pathology and Research. The Institute was originally the Inoculation Department of St Mary’s Hospital and was under the direction of Sir Almroth Wright, with whom Fleming worked closely.

In addition to a number of routine contributions to bacteriology and chemotherapy, Fleming made two important observations about antibiotic substances. In 1921 he noticed that his own nasal secretions dissolved (lysed) a colony of common bacteria on a Petri dish. He named the active substance lysozyme and discovered that it was also contained in other body fluids and in some plants. Lysozyme had no clinical application, however, as it was difficult to obtain in concentrated amounts and was ineffective against disease-causing bacteria.

In 1928, Fleming observed that a mould (later identified as Penicillium notatum) lysed colonies of the bacteria staphylococci, a common cause of wound infections. His paper describing this phenomenon mentioned the potential clinical importance of the substance, but he was unable to obtain penicillin in a sufficiently pure form to produce reliable results in patients with infections, and he abandoned his work in this area in the early 1930s. It was taken up again in World War II by a group at Oxford University, including the pathologist Howard Florey and the chemist Ernst Chain. This group succeeded in producing small amounts of penicillin and in demonstrating its effectiveness against a number of bacterial diseases. Industrial production methods were developed in the United States during the War.

Fleming, who was knighted in 1944, shared the 1945 Nobel Prize for Medicine or Physiology with Florey and Chain. Primarily through the publicity activities of Wright, Fleming received most of the popular acclaim for penicillin’s discovery.