When Alexander Fleming noticed the unusual contaminated culture plate, he reportedly said, “That’s funny.”
The plate contained staphylococci that had been contaminated by a blue-green Penicillium mould. Fleming and his colleague Stuart Craddock—or, in some accounts, the laboratory assistant Merlin Pryce—noticed that the bacteria immediately surrounding the mould had failed to grow, while colonies farther away remained visible. Fleming’s brief reaction captured the unexpected nature of the observation.
He photographed the plate and preserved a sample of the mould before investigating it further. Subsequent experiments showed that the mould released an antibacterial substance into the surrounding medium. Fleming later named that substance penicillin, a word he coined on 7 March 1929.
The famous remark should not be mistaken for the entire discovery story. Fleming did not instantly produce a usable drug from one contaminated plate. His work established the antibacterial effect, while Howard Florey, Ernst Chain, Norman Heatley, and others later developed purification, testing, and production methods that made clinical treatment possible.