Narrator: This is Science Today. In the last 10 years, there's been a dangerous rise in drug-resistant infections in major U.S. hospitals. Epidemiologist Lee Riley of the University of California, Berkeley says one bacteria, enterococcus, is now untreatable by even the strongest known antibiotic, vancomycin. And that's because vancomycin has been prescribed so heavily it's knocked out weaker mutations of enterococcus until only the strongest form remains.

Riley: The original reason for the use of vancomycin was because of the so-called staphylococcal infections. Staphylococcal infection is a very common infection in hospitals. The organism went through a series of antibiotics, and so vancomycin eventually became the last resort for treatment of staphylococcal infections.

Narrator: But in the meantime, enterococcus appeared in hospitals and went through a similar series of mutations...

Riley: ... and this organism has already become resistant to vancomycin. So the concern right now is -- in all the hospitals this is a major fear -- is seeing the appearance of staphylococcus that's become resistant to vancomycin. If that happens, a lot of people are going to be worried...

Narrator: ...because staph infection will be untreatable. For Science Today, I'm Steve Tokar