What is the name of the first antibiotic discovered?

The first antibiotic discovered is generally identified as penicillin. In 1928, Scottish physician Alexander Fleming observed that a Penicillium mould contaminating a bacterial culture prevented nearby bacteria from growing, and he named the antibacterial substance penicillin.

Fleming's discovery was an important beginning, but penicillin did not immediately become a practical medicine. During the late 1930s and early 1940s, researchers at Oxford, including Howard Florey and Ernst Chain, developed methods to purify and test it. Their work helped turn Fleming's observation into a usable treatment for serious bacterial infections.

The phrase “first antibiotic” is sometimes used loosely because earlier antimicrobial drugs existed, including Salvarsan. However, penicillin is the standard answer in general-knowledge quizzes because it was the first widely recognized naturally derived antibiotic and launched the antibiotic era. Amoxicillin is a later penicillin-family drug, while streptomycin and tetracycline were discovered afterward.