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Two strains of C. difficile caused global epidemic, study shows

December 10, 2012|By Eryn Brown
  • Stained Clostridium difficile bacteria. Hardy spores from two strains of the pathogen caused a global epidemic from 2002 to 2006, researchers said Sunday.
Stained Clostridium difficile bacteria. Hardy spores from two strains… (David Goudling )

Scientists said Sunday that the Clostridium difficile epidemic from 2002 to 2006 — an outbreak of gastrointestinal illness that spanned hospitals across the globe — was caused by two closely-related strains of the bacterium and not one, as had been previously believed.

Trevor Lawley of the Wellcome Trust Sanger Institute in Hinxton, England and coauthors from other institutions sequenced the genomes of C. difficile samples collected between 1985 and 2010, mainly from hospital patients. 

Analyzing the samples, they found the two lineages of the bacterium,which they named FQR1 and FQR2. Both strains originated in North America and developed the same mutation independently to become resistant to the antibiotic fluoroquinolone (which until that period had been an effective treatment for C. difficile infection). This acquired resistance to the drug may have helped the bacterias’ spores spread over vast geographic distances, the team wrote (subscription required) in the online edition of the journal Nature Genetics

FQR1 seemed to have emerged in the U.S., spreading from Pennsylvania to Oregon, New Jersey, Arizona and  Maryland between 2001 and 2007.  It appeared sporadically in South Korea and Switzerland as well, between 2007 and 2010.  FQR2 had a broader distribution, most likely starting out in Canada and spreading rapidly into continental Europe, the U.K. and Australia.  The scientists concluded that the bacterium was introduced once into Australia and at least four separate times each into Europe and the U.K.

The research underscores concerns about antibiotic resistance — the process whereby pathogens mutate and become impervious to medical treatment.   Often, antibiotic resistance results from overuse or improper use of antibiotics.  (For more on antibiotic resistance, visit the website of the Center for Disease Dynamics, Economics & Policy in Washington, D.C., which has done extensive research on the problem. )

According to the Nature Genetics paper, “fluoroquinolone antibiotics were one of the most commonly prescribed antibiotic classes in North America during the late 1990s and early 2000s.” This, the coauthors said, would have encouraged the proliferation of the resistant strains and explained the simultaneous energence of more than one resistant type.

“We have exposed the ease and rapidity with which these fluorquinolone-resistant C. difficile strains have transmitted across the world,” said Lawley in a statement. He suggested that the genome sequencing performed by the research group “heralds a new era of forensic microbiology for the transmission tracking of this major global pathogen.”

In the U.S., infection with C. difficile, which results in inflammation of the colon, causes diarrhea linked to 14,000 deaths every year, according to the U.S. Centers for Disease Control.  The bacterium is shed in feces and can live for long periods on surfaces.  Patients usually become infected when a healthcare worker passes it along after touching a contaminated surface or item, the CDC explains here.  

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