Penicillin was discovered by:

Scottish bacteriologist Alexander Fleming, in September 1928 at St. Mary's Hospital in London, made a remarkable discovery. He found a mold, Penicillium notatum, which had contaminated one of his bacterial culture plates and was destroying the nearby colonies of Staphylococcus. Fleming's discovery of penicillin is not the end of the story, as Florey and Chain went on to purify it.