Fleming, Sir Alexander (1881-1955), was a British bacteriologist at St. Mary's Hospital at the University of London. In 1928, he discovered the germ-killing power of the green mold, Penicillium notatum, from which the life-saving antibiotic, penicillin, was first purified (see Antibiotic; Penicillin). For his discovery, Fleming shared the 1945 Nobel Prize in medicine with British scientists Howard Florey and Ernst B. Chain. Florey and Chain helped develop the use of this drug (see Florey, Lord; Chain, Ernst Boris).