Penicillin Discovered

Penicillin, the first true antibiotic, was discovered when the Scottish bacteriologist Alexander Fleming noticed that a mold contaminating one of his bacterial cultures had killed the bacteria around it. The observation, made at St Mary's Hospital in London, opened the way to modern antibiotic medicine. The date is often given as 1928, since Fleming's own account and his 1929 publication point to that period, but the event is commonly dated to the late 1920s, and some historians have questioned the exact timing. What is not in doubt is that this chance sighting eventually transformed the treatment of infectious disease.

In the early twentieth century, bacterial infections were among the leading causes of death. A scratch, a surgical wound, pneumonia, or childbirth could prove fatal, and doctors had few effective treatments. Fleming had already seen the horrors of infected wounds as a medical officer in the First World War, and he had earlier discovered lysozyme, an enzyme in tears and saliva with mild antibacterial properties. He was therefore alert to substances that could attack bacteria.

According to the familiar story, Fleming returned from a holiday to find that a culture plate of Staphylococcus bacteria had been contaminated by a mold, and that the bacteria near it had dissolved. He identified the mold as belonging to the genus Penicillium and named the active substance penicillin. Details of the story, including how the spore arrived and what the weather was like, remain debated, and the tidy version has probably been simplified over time. Fleming published his findings in 1929, noting that the substance might have antiseptic uses, but he struggled to purify it and did not develop it into a drug.

That step came in the late 1930s and early 1940s at Oxford, where Howard Florey, Ernst Chain, and their colleagues, including Norman Heatley, worked out how to extract and concentrate penicillin and showed that it could cure infections in animals and then in people. With Britain at war, production moved to the United States, where companies scaled up manufacturing using deep-tank fermentation. By the later stages of the Second World War, penicillin was saving the lives of wounded soldiers. Fleming, Florey, and Chain shared the Nobel Prize in Physiology or Medicine in 1945.

The consequences were immense. Penicillin and the antibiotics that followed made once-deadly infections treatable and made surgery, cancer treatment, and organ transplants far safer. Estimates of lives saved are necessarily rough, but they run into the many millions. The legacy is also cautionary: bacteria evolve resistance, and Fleming himself warned that misuse could breed resistant strains. Antibiotic resistance is now a serious global health concern.