National Geographic : 2011 Jun
NEXT PHOTO: SCIENCE PICTURES, LTD./PHOTO RESEARCHERS, INC. A Helping Hand The surface of human skin is crowded with bacteria that would, if your immune system allowed it, cause serious infection. But researchers at the University of Califor- nia, San Diego, have discovered that one bacterium in that mix, Staphylococcus epidermidis (a close cousin of methicillin-resistant S. aureus, or MRSA) may actually help fine-tune the immune system. To do its good work, S. epidermidis deploys a molecule that blocks aggressive inflammatory agents. If unchecked, those agents would ignite a rashy reaction around even a minor scrape. Good staph stays good only if locked outside by the skin's multiple defenses, though. Give that germ a way into a weakened body---like a ride on a surgical implant---and it can ignite a potentially fatal infection. ---Vikki Valentine Staphylococcus epidermidis is a common form of bacteria found on human skin. Invisible to the eye, bacteria are revealed when a handprint made in agar gel (above) is cultured in a laboratory.