penicillum

The Latin word penicillus means 'little brush' or 'pencil.' The Romans used it to describe a fine, tapering implement for writing or painting. When Alexander Fleming returned from holiday on September 28, 1928, to his laboratory at St. Mary's Hospital in London, he noticed something odd: a mold had contaminated one of his bacterial culture plates, and around the mold, the bacteria had died. He examined the mold under a microscope and saw it was shaped like a tiny brush. He named it Penicillium notatum.

Fleming had been studying Staphylococcus bacteria for years, searching for an antibacterial agent. The contamination was an accident—but Fleming had trained himself to notice what others missed. He cultured the mold and discovered it secreted a powerful substance that killed many harmful bacteria without poisoning human cells. He called the substance penicillin, preserving the Latin root of the mold's name.

For over a decade, penicillin remained a laboratory curiosity. Fleming published his findings in 1929, but the scientific community was skeptical. In 1939, as World War II began, Howard Florey and Ernst Boris Chain at Oxford rediscovered Fleming's work. Florey's team purified penicillin and tested it on mice infected with deadly Streptococcus. The results were miraculous: infected mice treated with penicillin survived; untreated mice died.

By 1941, penicillin was being mass-produced. The drug reached the battlefield and saved countless soldiers from amputation and death due to infected wounds. A word born from Latin's word for a painter's brush became synonymous with modern medicine. Fleming won the Nobel Prize in 1945. The mold's shape had named itself into history.