Antibiotic-eating germ alarms doctors.

For 50 years, doctors have been assailing bacteria with the best antimicrobials science can devise, but the bugs have shown a remarkable ability to adapt to the onslaught. Bacteria not only survive, they thrive. Worse, they continue to feast on people, which is why doctors are so concerned about antibiotic-resistant microbes.

Now, researchers at St. George's Hospital Medical School in London say they have isolated a bacterium from two patients that is not only resistant to an antibiotic but actually dependent upon it. This bacterium, a strain of Enterococcus faecium, cannot survive without a steady diet of vancomycin, report Nadia Farrag, Ian Eltringham, and Helen Liddy in the Dec. 7 Lancet. This finding suprised the researchers because vancomycin is one of the most potent antibiotics known.

The two patients were men in their sixties. One had a ruptured esophagus that required emergency treatment, and the other had undergone prostate cancer surgery. Both developed Enterococcus infections and were treated with vancomycin. The antibiotic initially seemed to banish the infection, but the bugs bounced back. When researchers began testing the germs, they found the vancomycin-dependent strains, which alarmed them. "Have we at last witnessed the emergence of a true superbug?" the trio asked, tabloid-style, in Lancet.

Mark Wilks, a microbiologist at St. Bartholomew's Hospital Medical College in London, blames this "rhetorical flourish" for "elevating an interesting laboratory phenomenon to the status of yet another health panic."