February 28, 2012

‘Superbug’ Transfer: The Jump From Humans, to Animals, and Back

Chris Stevens

Chris Stevens

Communications Director

Center for a Livable Future

Methicillin-resistant Staphylococcus aureus

News media outlets throughout the nation were abuzz last week with the report of new scientific research showing, for the first time, how a strain of infectious Staph began life in humans, then spread to livestock where it became MRSA, and then jumped back to humans. The study was published Tuesday in the online journal mBio.

National Public Radio’s popular blog, The Salt, noted in its lead story Tuesday, that “Researchers have nailed down something scientists, government officials and agribusiness proponents have argued about for years: whether antibiotics in livestock feed give rise to antibiotic-resistant germs that can threaten humans.”

“Finally, a smoking gun connecting livestock antibiotics and superbugs,” said a headline in the online environmental publication Grist, written by contributing writer Tom Laskawy. As one who has covered the topic for years, Laskawy was not understating the importance of the research.

The breakthrough research has been a long time coming. For years, the livestock industry has insisted no conclusive evidence existed to link the overuse of antibiotics to antimicrobial resistance in humans. The connections have been long suspected. Several studies—many supported by the Center for a Livable Future—have focused on the impacts of the overuse of important human antibiotics in livestock production.

When the news release announcing the published research arrived, it was no great surprise to see former CLF Doctoral Fellow Lance Price listed as the lead author. Lance, 43, who earned his PhD at Johns Hopkins Bloomberg School of Public Health, now serves as associate professor at the Translational Genomics Research Institute in Arizona, where he directs the Center for Food Microbiology and Environmental Health. Much of his past CLF funded research focused on the transfer of antibiotic resistant genes in agriculture.

Lance is passionate when discussing the implications of the study. “ Just as the introduction of antibiotics was a miracle, the loss of their effectiveness would be a total disaster, ” he says, emphasizing “disaster.” Lance calls the cycle he and he co-researchers uncovered—which traced the development of MRSA CC398 from human, to livestock, and back to human—one which is “really interesting.”

“Our findings underscore the potential public health risks of widespread antibiotic use in food animal production. Staph thrives in crowded and unsanitary conditions. Add antibiotics to that environment and you’re going to create a public health problem.

“Retracing the evolutionary history of MRSA CC398 is like watching the birth of a superbug — it’s simultaneously fascinating and disconcerting,” says Lance. “MRSA CC398 was discovered less than a decade ago and it appears to be spreading very quickly.”

The possibility of a superbug infecting an increased number of people only increases, according to concerned scientists, with an estimated 80 percent of the antibiotics produced in the US used in food animal production.

This research project was somewhat more challenging that those Lance had been involved with before. The magnitude and scope of this study alone­—an enormous project involving researchers at 20 institutes who worked together to study 89 genomes from humans and animals from 19 countries and four continents—was challenging, according to Lance. “It was a real collaboration—working with 30 authors, and people contributing strains from all over the world.”

Showing the transfer of the strains required tools and techniques that have only been developed recently. “The standard typing methods can’t differentiate the strains,” noted Lance. “Only by applying the whole genome sequence-based analyses were we able to understand what was happening.” Whole genome sequencing, a cutting-edge testing method in which billions of molecules of DNA are spelled out in detail, enabled the scientists to trace the likely history of MRSA CC398.

What does this research mean for public health? As an example, Lance looks toward the Netherlands—a country he notes that is good at controlling the overuse of antibiotics in its human population, but not so good at controlling antibiotic use in food-animal production. Most of the early reports of the MRSA CC398 strain could be traced back to individuals with exposure to livestock. But increasingly strains are showing up in people who have had no exposure to livestock. “Data from Netherlands shows it emerging rapidly, changing in prevalence in people is perhaps evidence it’s being transferred people to people.”

Next month, Lance and other researchers will be discussing the issue of antibiotic resistance with US legislators at a Congressional briefing sponsored by the Center for a Livable Future and the Center for Science in the Public Interest (CSPI).

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