Florey credited René 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, tyrothricin, a compound of 20% gramicidin and 80% tyrocidine, from Bacillus brevis.
Florey acknowledged René Dubos' pioneering work in systematically searching for antibacterial compounds, which led to the discovery of gramicidin and revitalized Florey's research on penicillin. In 1939, coinciding with the start of World War II, Dubos reported the discovery of the first naturally derived antibiotic, tyrothricin, a compound of 20% gramicidin and 80% tyrocidine, from Bacillus brevis.