The dirty dish that saved millions of lives
In 1928, biologist Alexander Fleming returned to his cluttered London laboratory after a vacation. He noticed that one of his petri dishes, left unwashed, had grown a blue-green mold. Crucially, the bacteria surrounding the mold had been destroyed. Fleming identified the mold as Penicillium, leading to the world's first mass-produced antibiotic. His messy habit turned a ruined experiment into one of medicine's greatest breakthroughs.
An Overlooked Culture Dish in London
In late summer of 1928, Alexander Fleming, a Scottish physician and microbiologist working at St Mary's Hospital in London, left his laboratory for a family vacation. On his workbench sat a collection of Petri dishes inoculated with Staphylococcus bacteria, a common pathogen responsible for boils, sore throats, and wound infections. Fleming was known among his peers as a brilliant researcher whose laboratory was often disorganized. Rather than storing or cleaning his culture plates before departing, he stacked them in a quiet corner of the room, leaving them exposed to the ambient air and temperature fluctuations of the late summer.
Upon his return in September, Fleming began sorting through the discarded plates to evaluate them before decontamination. One culture caught his attention because it had been contaminated by a stray fungal spore. Surrounding the patch of blue-green mold was a distinct, transparent halo where the colonies of Staphylococcus had completely disintegrated or failed to grow. Further away from the mold, the bacterial colonies remained thick and healthy. Fleming recognized that the mold was producing a diffusible substance that actively killed or lysed the surrounding bacteria.
Fleming identified the mold as belonging to the genus Penicillium, later identified specifically as Penicillium rubens (initially classified as Penicillium notatum). He began culturing the fungus in liquid broth, discovering that the filtered broth retained its antibacterial potency even when diluted hundreds of times. He coined the name 'penicillin' to describe the antibacterial substance produced by the mold filtrate. In 1929, Fleming published his initial observations in the British Journal of Experimental Pathology, noting that the broth was non-toxic to human white blood cells and laboratory animals, though he struggled to isolate the chemically unstable active ingredient.