Antibiotics were present in ancient times in the form of molds. British scientist Sir Alexander Fleming discovered penicillin, the first working agent that demonstrated potent antibacterial properties, in 1928. Selman Waksman coined the term antibiotic in 1941, according to the National Center of Biotechnology Information, National Institutes of Health.
In the 19th century, several scientists, including Joseph Lister, John Tyndall and Joseph Tyndall, observed the antibacterial action of the Penicillium fungus in the human body, according to About.com Inventors. In 1904, Paul Ehrlich proposed the idea of a "magic bullet," a substance that targets the disease-causing microbes only, much like antibiotics. The drug, sold under the brand name Salvarsan, was the most frequently prescribed drug until penicillin became widely manufactured in the 1940s.