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Researcher Identifies Origins of a Super-Bug

Bacteria have interacted with humans throughout history, causing epidemics and plagues. If you look carefully in the historical record, you can even make an educated guess as to what bacteria might have caused illnesses long ago.

Scientist Frank DeLeo of the U.S. National Institutes of Health points to a passage in the Biblical Book of Job that includes a description of what is very likely the common bacteria Staphylococcus aureus. "'My body is covered with scabs and pus runs out of my sores,' and it's from Job 6:5." DeLeo says that describes what Staph aureus does. "It really causes abscesses and eschar — these scabs over these abscesses. You have dead white cells and bacteria that can burst forth from these areas of infection."

But DeLeo and his colleagues at the NIH wanted to know about a bacteria that's circulating in the United States and other western countries right now. It's a particular strain of Staph aureus called methicillin resistant Staph aureus or MRSA. It has the name because it's resistant to the antibiotics designed to stop it.

For about 40 years, MRSA was most common in hospitals and other health care environments. But since about 1998, DeLeo says, MRSA infections have become more common in the community, outside health care settings.

"These infections occur in people who are otherwise healthy," DeLeo says. "[In these patients] there's no obvious risk factors for MRSA. They haven't been in the hospital within a year, they haven't had surgery, they appear otherwise healthy and yet they're getting these infections which in the past were methicillin susceptible Staph aureus."

DeLeo and his colleagues studied the DNA from samples of MRSA sent to them from all over the U.S. They were asking one basic question: Is this particular strain of bacteria something that mutated once and then spread widely, or did many different Staph aureus strains develop methicillin resistance simultaneously?

They got their answer, DeLeo says, and it was definitive.

"It was the definitive proof that there was a single clone," DeLeo says. "There was a single bacterium that somehow, by some yet to be determined mechanism — it could be random — emerged and it had this combination of special characteristics that made it successful." So successful that it spread rapidly across the United States.

DeLeo says with this knowledge, scientists can create better tests to identify MRSA. And, he says, there's the possibility that eventually, someone could use this information to create a more effective antibiotic to fight it.

DeLeo's research is published in the Proceedings of the National Academy of Sciences.