The correct answer to this open question is the following.
Alexander Fleming ( 1881-1955) was a Scottish scientist who specialized in the field of bacteriology. He spent his life in the laboratory, studying infections in the human's saliva and tears. His major discovery was Penicillin, in 1928, and at that moment he became part of human history.
Due to that great discovery, Alexander Fleming revolutionized the pharmaceutical industry and the use of antibiotics saved millions of lives around the world. That is why, in 1945, he was awarded the Nobel Prize for Medicine. He shared this prize with pathologist Howard Florey and biochemist Boris Chain.
Through his research, Alexander Fleming discovered the way to prevent bacterial growth using penicillin, a strong antibiotic.