Fleming's accidental discovery of penicillin from this common mold revolutionized medicine. The specific strain's enzymes create chemicals that disrupt bacterial cell wall synthesis. A biochemical trick that saved millions of lives.
Official photographer, Public domain, via Wikimedia Commons
The Serendipitous Spore
In September 1928, the bacteriologist Alexander Fleming returned to his laboratory at St. Mary's Hospital in London after a holiday. He found a stack of petri dishes he had been using to culture Staphylococcus aureus, a bacterium responsible for abscesses and sore throats. One dish had been accidentally contaminated with a fungus, and around this blob of mold was a clear, bacteria-free zone. Fleming realized that the mold was producing a substance that inhibited the bacteria's growth.
The fungus was identified as a member of the Penicillium genus, specifically a variant now known as Penicillium rubens. Fleming named the bacteria-killing substance "penicillin." He published his findings in the British Journal of Experimental Pathology in 1929, but the scientific community showed little interest. The primary challenge was isolating the active substance in a stable form; early attempts to do so failed, and penicillin was considered a laboratory curiosity for nearly a decade. Fleming himself was unable to purify the compound, and its therapeutic potential remained untapped.
From Lab Bench to Lifesaver
The work on penicillin was revived in 1939 at the Sir William Dunn School of Pathology at the University of Oxford. A team led by pathologist Howard Florey and biochemist Ernst Boris Chain began to investigate penicillin's properties. An important member of their team, biochemist Norman Heatley, developed a back-extraction technique that allowed them to purify penicillin in usable, though still limited, quantities.
On May 25, 1940, the team conducted an experiment: they infected eight mice with lethal doses of streptococci bacteria. Four of the mice then received penicillin injections. The next morning, the untreated mice were dead, while the four that received penicillin survived. This success led to the first human trial in February 1941. The patient, a police constable named Albert Alexander, showed remarkable improvement initially. The team's small supply of the drug ran out after five days, and he ultimately died from the infection.
The demands of World War II created an urgent need for antibacterial agents. Florey and Heatley traveled to the United States in 1941 to seek help with mass production. Collaboration with American pharmaceutical companies and the USDA's Northern Regional Research Laboratory in Peoria, Illinois, led to breakthroughs. A more productive strain of the mold, Penicillium chrysogenum, was found on a cantaloupe in a Peoria market. By the D-Day landings in June 1944, enough penicillin was being produced to treat all Allied casualties. For their work, Alexander Fleming, Howard Florey, and Ernst Chain shared the 1945 Nobel Prize in Physiology or Medicine.
💡Fun Facts
Early supplies of penicillin were so scarce that it was collected from patients' urine to be re-administered, as up to 80% of a dose is excreted.
The chemical structure of penicillin was a closely guarded secret during WWII; scientist Dorothy Hodgkin finally determined it using X-ray crystallography in 1945.
The term "penicillin" originates from the Latin word *penicillus*, meaning "painter's brush," which describes the shape of the mold's spore-producing structures.
The strain of mold found on a cantaloupe in Peoria, Illinois, was found to produce 200 times more penicillin than Fleming's original sample.
The Alexander Fleming Laboratory Museum is open Monday to Thursday, from 10:00 to 13:00. Visits can be arranged outside these hours by appointment. The museum is closed on public holidays.
Admission
Free.
Accessibility
The museum is located in a historic listed building and is accessed by stairs; there is no wheelchair access.
