In 1928 Alexander Fleming, working in London, noticed that a Penicillium mould contaminating a culture plate killed surrounding bacteria, identifying its antibacterial action. The substance was turned into a usable medicine in the early 1940s by Howard Florey, Ernst Chain and their Oxford team, who purified penicillin, demonstrated its clinical effect and worked with industry to scale up production in time for the Second World War. This opened the antibiotic era, in which previously fatal bacterial infections could be cured. Fleming, Florey and Chain shared the 1945 Nobel Prize.
By making many bacterial infections curable, antibiotics sharply reduced deaths from wounds and disease, reinforcing the viability of dense urban living where infectious disease had long taken a heavy toll.
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