MELVILLE, N.Y. - The type of antibiotic-resistant bacteria troubling a growing list of US communities appear to be caused by a single strain that is spreading with extraordinary ease, according to federal scientists studying the microbe.
Known as MRSA, for methicillin resistant Staphylococcus aureus, the bacteria have become so prevalent that the Centers for Disease Control and Prevention estimates an incidence of about 32 infections for every 100,000 people. That statistic was deemed astounding last year in an editorial published in the Journal of the American Medical Association.
MRSA is the subject of two federally sponsored investigations and a third smaller one, funded by the New York State Health Department, getting underway on Long Island. Understanding MRSA is important, medical investigators say, because of its capacity to thwart numerous classes of potent antibiotics.
Reporting in the Proceedings of the National Academy of Sciences, which appears today online, microbiologist Frank DeLeo found that a strain of MRSA dubbed USA300 is the so-called epidemic strain underlying cases of the bacterial infection isolated in communities nationwide.
The MRSA strain showing up in many gay San Francisco men is a subtype of USA300.
DeLeo said USA300 has numerous subtypes, all of which have emerged from the parent strain.
"We anticipate that new USA300 derivatives will emerge within the next several years and that these strains will have a wide range of disease-causing potential," said DeLeo, who conducts MRSA research at Rocky Mountain Laboratories in Hamilton, Mont.
MRSA infections usually look like boils or spider bites but are capable of transforming into painful abscesses when left untreated. In some instances the bacteria can remain confined to the skin, but in others the microbes can burrow into the body, triggering life-threatening infections. Hand hygiene is the primary way to avoid MRSA infections.
DeLeo's research, the first study to compare DNA fingerprints of the microbe from various parts of the country, traces the origins of community-acquired MRSA and resolves a heated scientific debate. His findings rule out the previously held notion that multiple strains of MRSA emerged randomly with similar characteristics.
Dr. Bruce Farber, who has a $200,000 New York State grant to analyze hospital-acquired MRSA, said USA300 has been evolving for decades. "It will always be challenging to stay ahead of the novel way that this organism is changing," he said.
Farber and colleagues will study the highly infectious bacterium in nine intensive care units on Long Island. He estimates the research will involve more than 5,000 patients.
MRSA was once a hospital-acquired organism. Now that it is spreading in communities, the bacteria are being brought into hospitals from the outside.
