The fungus Penicillium chrysogenum is the source of penicillin, the antibiotic that was viewed a miracle drug after mass production began in the 1940s. But its relatives can have quite different uses: Other species like P. roqueforti and P. camemberti are used to make cheese. Although Alexander Fleming is credited with discovering penicillin in 1928, Stephenson says it's possible that it was used far earlier. In ancient Egypt, he notes, moldy bread was sometimes pressed into wounds to deter infections.