The chemical structure of penicillin was determined by Dorothy Crowfoot Hodgkin in the early 1940s. Penicillin has since become the most widely used antibiotic to date, and is still used for many Gram-positive bacterial infections. A team of Oxford research scientists led by Australian Howard Florey and including Ernst Boris Chain and Norman Heatley devised a method of mass-producing the drug. Florey and Chain shared the 1945 Nobel prize in medicine with Fleming for their work. After World War II, Australia was the first country to make the drug available for civilian use. Chemist John C. Sheehan at MIT completed the first total synthesis of penicillin and some of its analogs in the early 1950s, but his methods were not efficient for mass production.
The challenge of mass-producing the drug was daunting. On March 14, 1942, the first patient was treated for streptococcal septicemia with U.S.-made penicillin produced by Merck & Co. Half of the total supply produced at the time was used on that one patient. By June 1942, there was just enough U.S. penicillin available to treat ten patients. A moldy cantaloupe in a Peoria, Illinois market in 1943 was found to contain the best and highest-quality penicillin after a worldwide search. The discovery of the cantaloupe, and the results of fermentation research on corn steep liquor at the Northern Regional Research Laboratory at Peoria, Illinois, allowed the United States to produce 2.3 million doses in time for the invasion of Normandy in the spring of 1944. Large-scale production resulted from the development of deep-tank fermentation by chemical engineer Margaret Hutchinson Rousseau.