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2:04 pm
Mon December 10, 2012

How A Superbug Traveled The World

Originally published on Wed December 12, 2012 7:06 am

Just as the name implies, Clostridium difficile is a difficult pathogen to beat. It causes a nasty infection in your gut, and it's often resistant to many antibiotics.

But C. difficile got even more troublesome about 10 years ago when a particularly virulent form of the bug cropped up in hospitals across the U.S and was no longer vulnerable to one of the most common classes of antibiotics.

These days antibiotic-resistant C. difficile is a superbug that kills nearly 14,000 Americans a year.

British geneticists just sequenced a bunch of these C. difficile strains from around the world. And, the genomic data chart how the drug-resistant bacteria arose in North America and then hopped to Europe, Australia and Asia.

The findings were just published in the journal Nature Genetics.

C. difficile infections usually occur in hospitals when patients have been treated with large doses of antibiotics. So Trevor Lawley and his team at the Wellcome Trust Sanger Institute sequenced the genomes of 151 C. difficile strains isolated from hospital patients between 1985 and 2010.

From the DNA sequences, they calculated that the highly virulent form of C. difficile first appeared in Pittsburgh around 2001. From there, it spread to Oregon, New Jersey, Arizona and Maryland, where it caused major hospital outbreaks in each state. Since 2007, the drug-resistant bacteria have also made appearances in South Korea and Switzerland.

The genomic data also showed that another superbug of C. difficile cropped up independently in the U.S. around the same time. The scientists can't pinpoint exactly where it originated, but they know it spread to Montreal in 2003 and the Netherlands in 2006.

This strain found its way to the U.K. on four separate occasions, likely triggering a large hospital outbreak that reached both London and Cambridge.

Lawley and his team also figured out how the superbugs picked up resistance to a common class of antibiotics called fluoroquinolones that includes such drugs as Levaquin and Cipro.

Both strains independently acquired a single mutation in an enzyme that binds fluroquinolones, and the strains also captured genes that pump antibiotics out of their cells.

American doctors heavily prescribed fluoroquinolones in the late 1990s and early 2000s. And, Lawley thinks this study is a cautionary tale about the risk of overusing antibiotics.

"The data indicated that antibiotic resistance can happen more frequently than we appreciated," Lawley tells Shots. "And, it will probably happen again."

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