Discoverer of penicillin Alexander Fleming warned against its overuse and the risk of resistant microorganisms as early as 1945, in his Nobel Prize lecture

"The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant.

Here is a hypothetical illustration. Mr. X has a sore throat. He buys some penicillin and gives himself, not enough to kill the streptococci but enough to educate them to resist penicillin. He then infects his wife. Mrs. X gets pneumonia and is treated with penicillin. As the streptococci are now resistant to penicillin the treatment fails. Mrs. X dies. Who is primarily responsible for Mrs. X's death? Why Mr. X whose negligent use of penicillin changed the nature of the microbe.

Moral: If you use penicillin, use enough"

Sir Alexander Fleming shared the Nobel Prize in Physiology or Medicine in 1945 with Howard Florey and Ernst Boris Chain for his discovery of the world's first antibiotic substance benzylpenicillin (Penicillin G) from the mould Penicillium notatum in 1928. He also discovered the enzyme lysozyme in 1923.

Fleming's Nobel Lecture reached from here:Nobel Lecture by Sir Alexander Fleming on December 11, 1945