Ninety-eight years ago this week, a London bacteriologist came back from summer holiday, started sorting through petri dishes he had left stacked on a bench, and noticed one that was speckled with Staphylococcus colonies everywhere except for a clear ring around a blob of mold. The American Chemical Society, which designated the discovery an International Historic Chemical Landmark, dates that moment to September 3, 1928. The bacteriologist was Alexander Fleming of St. Mary's Hospital in London.
That is the story most people know. The part that rarely survives the retelling is that Fleming's mold never produced enough penicillin to treat patients on any meaningful scale. The strain that eventually did come from a rotting cantaloupe bought at a fruit market in Peoria, Illinois.
A Contaminated Dish, a Clear Halo, and a Paper Almost Nobody Acted On
Fleming found that what he called mold juice could kill streptococcus, meningococcus, and the diphtheria bacillus. He handed two assistants, Stuart Craddock and Frederick Ridley, the job of isolating pure penicillin from it. The compound turned out to be so unstable that they could manage only crude solutions.
When Fleming published his findings in the British Journal of Experimental Pathology in June 1929, he gave penicillin's therapeutic potential barely a mention. For a while its most obvious use looked like a laboratory trick for separating penicillin-sensitive bacteria from resistant ones in mixed cultures. Harold Raistrick at the London School of Hygiene and Tropical Medicine tried to purify the compound and failed.
The mold itself has since been renamed twice. Fleming called it Penicillium notatum, textbooks later listed it as Penicillium chrysogenum, and a 2011 analysis reclassified the species as Penicillium rubens. In 2020, researchers at Imperial College London, the University of Oxford and CABI revived Fleming's original isolate, cataloged as IMI 15378, from a living culture collection and sequenced its genome. Writing in Scientific Reports, they reported that its main penicillin-producing genes differ at the amino acid level from the industrial strains later used in the United States.
The First Patient Recovered, Then Died When the Supply Ran Out
Penicillin became a drug only because Howard Florey, Ernst Chain and their colleagues at Oxford's Sir William Dunn School of Pathology picked it up again in 1939. Their animal and clinical work required up to 500 liters of mold filtrate a week, which they grew in bedpans, milk churns and food tins, tended by a team of women hired at two pounds a week.
On February 12, 1941, a 43-year-old policeman named Albert Alexander became the first person to receive Oxford penicillin. He had scratched the side of his mouth while pruning roses and developed abscesses affecting his eyes, face and lungs. Within days of injection, he improved dramatically. Then the supply ran out, and he died a few days later.
That failure was a manufacturing problem, not a pharmacological one, and Florey concluded that wartime Britain could not solve it.
A Peoria Fruit Market Solved What Oxford Could Not
Florey and biochemist Norman Heatley traveled to the United States in the summer of 1941 and were routed to the Department of Agriculture's Northern Regional Research Laboratory in Peoria. Within weeks, Andrew Moyer found that replacing the sucrose in the culture medium with lactose raised yields. Adding corn steep liquor, a byproduct of corn wet milling that the lab had been trying to find a use for, raised them roughly tenfold.
The bigger obstacle was that Florey's strain produced only traces of penicillin when grown submerged in a tank rather than on the surface of a broth. Soil samples were shipped to Peoria from around the world in search of a better producer. The winner turned up locally, on a moldy cantaloupe from a Peoria fruit market. Irradiating that strain with X-rays at the Carnegie Institution, and later with ultraviolet light at the University of Wisconsin, pushed output higher still.
The numbers that followed are worth sitting with. U.S. penicillin production went from 21 billion units in 1943 to 1,663 billion in 1944 and more than 6.8 trillion in 1945. The price fell from twenty dollars per 100,000 units in 1943 to less than ten cents by 1949. Fleming, Florey and Chain shared the 1945 Nobel Prize.
Ninety-Eight Years On, One in Six Infections No Longer Responds
The era that opened with a contaminated dish is now closing in places. In its Global Antibiotic Resistance Surveillance Report 2025, released in October 2025, the World Health Organization reported that roughly one in six laboratory-confirmed bacterial infections worldwide in 2023 involved bacteria resistant to antibiotic treatment. Resistance rose in more than 40 percent of the pathogen and antibiotic combinations tracked between 2018 and 2023, at an average of 5 to 15 percent a year.
The burden is uneven. WHO estimated that one in three reported infections was resistant in its South-East Asian and Eastern Mediterranean regions, and one in five in the African region. In the United States, the Centers for Disease Control and Prevention attributes more than 2.8 million resistant infections and over 35,000 deaths a year to antimicrobial resistance, based on its 2019 Antibiotic Resistance Threats Report.
The genome work does not solve that. Its authors framed it as a starting point, noting that the wild Fleming strain and the heavily selected American strains arrived at penicillin production by different genetic routes, which might point to unexplored ways to engineer the pathway. Whether that leads anywhere useful is still unknown.
What the history does make clear is that the discovery and the cure were two separate problems, separated by thirteen years, an ocean and a piece of spoiled fruit. Anyone with a suspected bacterial infection should be evaluated by a clinician rather than self-treating, and leftover antibiotics should never be reused.
Key Questions Answered
What exactly did Fleming see on September 3, 1928? A petri dish of Staphylococcus colonies with a clear zone around a mold contaminant, suggesting the mold was releasing something that stopped bacterial growth.
Why did Fleming's own mold not become the source of the drug? It was unstable, hard to purify, and a poor producer in the large submerged tanks needed for industrial output. His team could make only crude preparations.
Where did the cantaloupe come from? A fruit market in Peoria, Illinois, near the Department of Agriculture laboratory that was screening soil and produce samples from around the world for higher-yielding Penicillium strains.
What happened to the first patient treated with penicillin? Albert Alexander, a British police officer, improved sharply after treatment in February 1941 but died after the limited supply of the drug was exhausted.
How common is antibiotic resistance now? WHO estimated that about one in six laboratory-confirmed bacterial infections worldwide in 2023 were resistant to treatment, with resistance rising in over 40 percent of monitored drug and pathogen combinations.
