In 1928, the Scottish physician and microbiologist Alexander Fleming made a landmark discovery at St Mary's Hospital in London that would fundamentally alter the course of modern medicine. Upon returning from a holiday, Fleming observed that a culture plate of Staphylococcus bacteria had been contaminated by a mould, later identified as Penicillium notatum. He noted that the bacteria in the immediate vicinity of the mould had been destroyed, revealing the potent antibacterial properties of the substance the mould produced. Fleming named this active agent penicillin, marking the beginning of the antibiotic era.

Although Fleming recognised the potential of his discovery, the transition from a laboratory observation to a life-saving clinical treatment required significant further development. The substance proved difficult to isolate and stabilise in sufficient quantities for therapeutic use. It was not until the late 1930s and early 1940s that a team of researchers at the University of Oxford, led by Howard Florey and Ernst Chain, successfully purified penicillin and demonstrated its efficacy in treating bacterial infections in both laboratory animals and human patients. This collaborative effort transformed a chance observation into a practical, mass-produced medicine.

The subsequent industrial-scale production of penicillin during the Second World War proved to be a turning point in global health, saving countless lives by providing an effective treatment for previously fatal bacterial infections. The development of this antibiotic revolutionised the management of wounds, surgery and infectious diseases, establishing a new standard for clinical care. The significance of this breakthrough was formally recognised in 1945, when Fleming, Florey and Chain were jointly awarded the Nobel Prize in Physiology or Medicine for their collective contributions to the discovery and development of penicillin.

• Discovery of antibacterial mould by Alexander Fleming in 1928.
• Identification of Penicillium notatum as the source of the active agent.
• Successful purification and testing by the Oxford team led by Florey and Chain.
• Mass production and clinical application during the Second World War.
• Awarding of the Nobel Prize in 1945 for the discovery and development of the drug.