Natural antibiotic found on human skin.

Human skin produces a natural antibiotic that protects it against bacterial infection, according to a new study. Dermatologists at the University of Kiel in Germany identified a small protein, called human beta-defensin-2, that kills bacteria such as Escherichia coli and Pseudomonas aeruginosa as well as the common yeast Candida albicans.

The protein punches holes in the membranes of the bacteria, making them "look like a sieve," says chemist Jens-Michael Schroder. "The strategy to kill the bacteria is totally different from other antibiotics because they do it mechanically," rather than biochemically. By exploiting the newly discovered strategy, scientists might be able to avoid the problem of bacteria developing drug resistance.

Schroder, and his colleagues began with the observation that patients with psoriasis--an inflammatory disease that causes large amounts of skin to scale off--rarely developed infections despite ever-present injuries to their skin. They analyzed skin cells from patients in their clinic and eventually identified defensin as an antimicrobial agent. The researchers then found the same defensin in patients' lungs and throats, they report in the June 26 Nature.

The antibiotic closely resembles one found on the tongues and throats of cattle (SN: 3/18/95, p. 166). Humans also produce another antibiotic, human beta-defensin-1, in the urogenital tract. What makes human beta-defensin-2 different, Schroder says, is that it is only made when bacteria are present.

The researchers are now looking for additional antibiotics, especially ones that defend against bacteria such as Staphylococcus aureus.