Mutation to blame for staph outbreak, research says

HELENA - Frank DeLeo, a researcher at Rocky Mountain Laboratories in Hamilton, doesn't mince words when he talks about what's happening with staph infections in America.

“It's an epidemic, actually,” the scientist said in an interview from his Bitterroot Valley lab, which is doing some of the foremost research on the newly potent disease.

This week, DeLeo and his team unveil their latest findings: They have shown that the staph infections now killing more Americans than AIDS are caused by a single strain of the bacterium, known as USA300.

Their findings are presented in a paper published this week in the online edition of Proceedings of the National Academy of Sciences.

Rocky Mountain Labs is a federal research institution run by the National Institute of Allergy and Infectious Diseases, an arm of the federal National Institutes of Health.

Staphylococcus aureus is an extremely common bacterium. If you gave every human being a nasal swab, up to 30 percent would turn up colonies of staph, although very few of those cases would ever cause disease.

Five years ago, though, something happened to staph. The disease best known for boils and other minor skin infections started causing more invasive, violent attacks. It also proved immune to many traditional, antibiotic medicines and seemed to spread more easily than before.

This staph is not the same kind of antibiotic-resistant staph long present in hospitals, where antibiotic use is high, DeLeo said. This epidemic emerged in society at large and is now spreading into hospitals.

DeLeo and his colleagues have been working for years to understand the bug and why it causes serious, even deadly, diseases where its staph grandparents did not.

Researchers and doctors call the bacterium CA-MRSA, for “community-associated methicillin resistant Staphylococcus aureus.”

Methicillin is a second-generation antibiotic that came into the fore in the 1960s, after bacteria became immune to penicillin. Methicillin has since been replaced by other antibiotics, although its name lives on in the MRSA acronym.

Drug resistance, however, is not what makes CA-MRSA so awful. DeLeo's work, and that of others at Rocky Mountain Labs, have shown that CA-MRSA lays waste to the body's frontline immune system cells, sometimes “ganging up” on the best disease killers.

The bacterium can also “blow up” the immune system cells sent to destroy it.

DeLeo and his colleagues are continuing their research into what makes CA-MRSA so potent, but they also wanted to find out where the strain came from. They wanted to test the idea that several strains, emerging simultaneously with very similar attributes, were behind the epidemic. To do so, they got samples from 10 sick patients around the country and mapped all the genes of the samples. Previous studies had looked only at a few genes.

Eight of the 10 samples had nearly identical genes, suggesting a common parent. The other two were also related, although not as closely.

One curious finding: Of the eight samples that were almost identical, two caused much more serious disease than the others. This suggests that even slight genetic changes can lead to more dangerous bacteria, according to the study.

This is not the first time staph has outsmarted medicine. The germ became resistant to penicillin in the 1940s, according to the paper. Later, in the 1950s and 1960s, a penicillin-resistant strain caused pandemic disease.

In those cases, DeLeo said, a new strain of staph emerged uniquely outfitted to spread and make people sick.

Following a pattern, the strains eventually played themselves out. DeLeo forecasts something similar for the current epidemic.

He said diluted, less violent strains of MRSA are already showing up, suggesting the disease may be in the early stages of waning. Still, that is little comfort for the tens of thousands of Americans sickened by MRSA, thousands of whom can be predicted to die.

To help doctors in the midst of the epidemic, DeLeo said he and his colleagues are using their new knowledge to find ways to more quickly identify CA-MRSA.

He said the findings also shed light on how and why bacteria cause epidemic disease.

“We have these waves where one clone becomes really successful for some unknown reason, (then it) becomes diffused,” he said.

Copyright © 2009 Missoulian