The great modern advances in chemotherapy have come from the chance discovery that many microorganisms synthesize and excrete compounds that are selectively toxic to other microorganisms. These compounds are called antibiotics and have revolutionized medicine. The period since World War II has seen the establishment and extremely rapid growth of a major industry, using microorganisms for the synthesis of, amongst other compounds, chemotherapeutic agents. The development of this industry has had a dramatic and far-reaching impact. Nearly all bacterial infectious diseases that were, prior to the antibiotic era, major causes of human death have been brought under control by the use of chemotherapeutic drugs, including antibiotics. In the United States, bacterial infection is now a less frequent cause of death than suicide or traffic accidents.

The first chemotherapeutically effective antibiotic was discovered in 1929 by Alexander Fleming (1881-1955), a...