Health: Bad Bug Does Good; A benign bacteria that kills human pathogens could become the first in a new line of weapons--living antibiotics.(Cover Story)

Byline: Temma Ehrenfeld

Viruses like H5N1 don't respond to antibiotics, which makes them especially hard to fight. But plain old bacteria can be scary, too. The bacterium Bdellovibrio sounds like something out of a Stephen King novel. It likes to swim along until it collides with some unlucky single-celled creature. It gloms onto its victim's cell membrane, uses nasty enzymes to bore inside and then gorges itself on the innards, swelling to as much as 15 times its original size. Then it divides into as many as 15 little predator progeny, which swarm out of the empty husk in search of prey.

Luckily for us, Bdellovibrio doesn't have a taste for human cells, though it's been known to inhabit the human gut. But it's quite fond of human pathogens--bugs like salmonella and E. coli, which kill thousands each year, and which are also growing more and more resistant to antibiotics each day. The potential of Bdellovibrio as a weapon against bacterial infections may seem obvious, but until biochemist Stephan Schuster of the Max-Planck Institute in Tubingen, Germany, thought to look in 2002 nobody had studied the complete genome of this benign bug. Last week in the journal Science, Schuster and his colleagues published its genome and the first look at its lifestyle. "We see the potential to create a last-resort drug for patients whose immune systems have given up and are near death," says Schuster.

Bdellovibrio gets its name from the Greek "bdello," meaning to suck, and the Latin "vibrio," or curved rod, after its shape. What makes it so interesting from a medical point of view is that the bug would allow ...