Carl Zimmer in his blog, The Loom:
This story starts in 1987, with the skin of a frog.
Michael Zasloff, a scientist then at NIH, was impressed by how well a frog in his lab recovered from an incision he had made in its skin during an experiment. He kept his frogs in a tank that must have been rife with bacteria that should have turned the incision into a deadly maw of infection. Zasloff wondered if something in the skin of the frog was blocking the bacteria. After months of searching, he found it. The frogs produced an antibiotic radically unlike the sort that doctors prescribed their patients.
Most antibiotics kill bacteria by jamming up their enzymes. The bacteria can no longer copy its DNA or expand its membrane as it grows or do some other task essential to their survival, and they die. Zasloff and his colleagues figured out that the antibiotics in frog skin worked entirely differently. These small molecules were attracted to the positive charge on the surface of many species of bacteria. Once they stuck to the membrane, the frog molecules changed shape, so that they punched a hole through the membrane. The bacteria’s innards spilled out of the hole, leading to their death.
The antibiotics from frog skin proved to be just a tiny sampling of a huge natural pharmacy.