Antibiotic penicillin led to renewed interest in the search for antibiotic compounds with similar efficacy and safety. For their successful development of penicillin, which Fleming had accidentally discovered but could not develop himself, as a therapeutic drug, Chain and Florey shared the 1945 Nobel Prize in Medicine with Fleming. Florey credited Rene Dubos with pioneering the approach of deliberately and systematically searching for antibacterial compounds, which had led to the discovery of gramicidin and had revived Florey's research in penicillin. In 1939, coinciding with the start of World War II, Dubos had reported the discovery of the first naturally derived antibiotic,
Antibiotic prophylaxis to the serious problem of superbugs (which are bred in antibiotic-rich environments) the Food and Drug Administration issued a guidance document in December 2013. The chief public health officer of Canada said four months later that "antibiotics should only be used in animals to treat infection rather than guard against disease or promote growth." The Canadian guidance document calls for "the prudent use of antibiotics in animal agriculture and a gradual phasing out of growth promoting drugs in feed and water over the three years" ending in 2017. Producers will no longer be allowed to continuously feed animals doses of