In 1928 Scottish bacteriologist Alexander Fleming was in the process of sterilizing bacterial culture plates that had become contaminated with mold when he noticed clear zones circling mold colonies. The mold toxin responsible for killing the bacteria turned out to be penicillin, which Australian pathologist Howard Walter Florey and British biochemist Ernst Boris Chain later successfully isolated and purified to produce what became arguably the world’s most effective live-saving antibiotic. Incidentally, Fleming seemed to thrive on contamination—his other major discovery, of the antiseptic enzyme lysozyme in 1921, was made after he had accidentally contaminated a culture plate with his own cold germs.