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The tiny, spiny and adorable hedgehog is helping to upend conventional wisdom about the origins of drug-resistant bacterial infections that kill thousands of people each year.
In a study published Wednesday in Nature, a group of international scientists found that the bacteria that cause a tough-to-treat infection existed in nature long before modern antibiotics began to be mass produced in the 1940s. The drugs have saved countless lives, but the wide distribution of antibiotics in the decades since then has also spurred an evolutionary arms race with the pathogens they target, leading to the emergence of dreaded superbugs that have evaded our efforts to vanquish them with pharmaceuticals.
The key to the scientists’ paradigm-altering theory? Danish roadkill.
When researchers examined hundreds of dead hedgehogs from Denmark and other countries in Western Europe, they found MRSA, or methicillin-resistant staphylococcus aureus, living on the skin of the vast majority of the animals. That was surprising, given that the animals had not been exposed to penicillin, though MRSA does colonize many mammals, including humans, where they can live harmlessly inside the nose or on the skin. The danger arises when these bacteria enter the bloodstream through a wound or intravenous tube, with potentially deadly consequences for those with weakened immune systems.
The scientists were also intrigued by another pathogen they found on many of those same hedgehogs: a skin fungus that produces a penicillin-like substance which inhibits the growth of staphylococcus aureus. Like modern antimicrobials, this naturally occurring antibiotic is in constant battle with the staph bacteria that compete for nutrients on the hedgehog’s skin. Over time, some of those bacteria developed an ability to outsmart their fungal rivals and thrive on their hedgehog hosts, the study showed.
What likely happened next is a familiar tale in the annals of infectious disease. The particular strain of MRSA that colonized the hedgehogs, known as mecC-MRSA, later found its way to dairy cows in rural areas where both creatures flourish, and eventually to humans. In Denmark, mecC-MRSA sickens 10 to 30 people a year.
Through genetic coding of the hedgehog-borne mecC-MRSA, researchers were able to establish a timeline of its evolution back to the early 1800s, long before Alexander Fleming stumbled on a speck of mold in a petri dish that was repelling a spreading Staphylococcus colony.
Anders Rhod Larsen, a microbiologist and a lead author of the paper, said the findings added a new wrinkle to the predominant narrative that the overuse of antibiotics was solely responsible for the rise of superbugs. “The main message is that MRSA predates antibiotic use in humans, but the broader theme is that we are not alone in this world,” said Dr. Larsen, who leads the National Reference Laboratory for Antimicrobial Resistance at Statens Serum Institut in Copenhagen. “Antibiotic resistance does not have any boundaries and it can be transmitted between species.”
Researchers not involved with the study said the findings helped to confirm long-held assumptions about the dynamics of antibiotic resistance. Antimicrobial substances, after all, are abundant in nature, and bacteria and fungi have long found ways to outsmart these compounds.
Lance Price, who leads the Antibiotic Resistance Action Center at George Washington University, commended the research for documenting the process in the real world, and with such precision.
“This is such an interesting story because who doesn’t love hedgehogs,” he said. “But what’s important about this paper is it shows the natural evolution of a drug-resistant human pathogen.”
Tara C. Smith, an epidemiologist at Kent State University College of Public Health who studies livestock-associated MRSA, said the study helped highlight the role that animals played as reservoirs of antimicrobial resistance. “It really just steps up the need for better antibiotic stewardship and to take heed of what we’re using, both in human medicine and animal medicine,” she said.
The MRSA that infected the hedgehogs did not appear to sicken them, but its overwhelming presence on the animals sampled from Denmark largely corresponded with mecC-MRSA’s prevalence among humans in that country. First discovered in 2011, mecC-MRSA has since spread to dairy herds across northern Europe and it can sometimes cause infections in cows but has rarely sickened humans.
Jesper Larsen, another lead author of the paper and a senior researcher at Statens Serum Institut, said the results had already inspired him and other researchers to expand their focus on antibiotic resistance in wild animals. But he cautioned against any notion that naturally occurring resistance somehow lessened the urgency to curb the use of antimicrobial drugs to treat illness in humans.
“The lesson here is that when we overuse antibiotics, we accelerate what is already happening in nature,” he said.
There is perhaps another lesson from the study, Dr. Larsen added. Although the risks of humans contracting MRSA directly from hedgehogs are likely minimal, maintaining a healthy distance from the animals was always prudent.