Alexander Fleming discovers penicillin in 1928

On September 28, 1928, Scottish biologist and pharmacologist Sir Alexander Fleming discovered penicillin at St Mary's Hospital in London. While working in his laboratory, Fleming observed a blue-green mold, now known as Penicillium notatum, contaminating a staphylococcal bacterial culture. He noticed a clear zone around the mold where bacterial growth was inhibited, leading him to conclude that the mold released a substance capable of suppressing bacterial growth and dissolving bacterial cells.

While Fleming is credited with the discovery, the subsequent development of penicillin into a usable medicine is attributed to Nobel laureates Howard Florey and Ernst Chain. Historical records indicate that other researchers had noted the bacteriostatic effects of Penicillium earlier; John Tyndall published findings in 1875, and French physician Ernest Duchesne documented the lethal effects of certain molds on bacteria in 1894.

Fleming coined the term ‘penicillin’ to describe the filtrate from the mold culture. In its early stages, the substance proved most effective against Gram-positive bacteria, though it was ineffective against Gram-negative organisms.