The tiny, prickly, and adorable hedgehog is helping to turn conventional wisdom on its head 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 difficult-to-treat infection existed in nature long before modern antibiotics were mass-produced in the 1940s. The drugs have saved countless lives, but the widespread use of antibiotics in the decades since then has also spurred an evolutionary arms race with the pathogens they target, leading to the creation of dreaded superbacteria that have eluded our efforts to bring them with us Defeat Medicines.
The key to the paradigm-changing theory of scientists? Danish roadkill.
When researchers examined hundreds of dead hedgehogs from Denmark and other Western European countries, they found MRSA, or methicillin-resistant Staphylococcus aureus, which lived on the skin of the vast majority of the animals. This was surprising because the animals were not exposed to penicillin, even though MRSA colonizes many mammals, including humans, where they can live harmlessly in the nose or on the skin. The danger arises when these bacteria enter the bloodstream through a wound or an infusion tube, with potentially fatal consequences for people with compromised immune systems.
The scientists were also fascinated by another pathogen that they found in many of these hedgehogs: a skin fungus that produces a penicillin-like substance that inhibits the growth of Staphylococcus aureus. Like modern antibiotics, this naturally occurring antibiotic is in constant battle with the staphylococci that compete for nutrients on the hedgehog’s skin. Over time, some of these bacteria developed the ability to outsmart their fungal rivals and thrive on their hedgehog hosts, the study showed.
What likely happened next is a well-known story in the annals of infectious diseases. 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 thrive, and eventually to humans. In Denmark, mecC.-MRSA affects 10 to 30 people a year.
Genetically encoding the MecC.-MRSA, researchers were able to trace a timeline of its development back to the early 19th century, long before Alexander Fleming stumbled upon a mold in a petri dish that was fighting off a spreading staph colony.
Anders Rhod Larsen, microbiologist and lead author of the paper, said the results add a new wrinkle to the prevailing narrative that overuse of antibiotics is solely responsible for the rise in super bacteria. “The main message is that MRSA is older than antibiotic use in humans, but the more general issue is that we are not alone in this world,” said Dr. Larsen, who heads the National Reference Laboratory for Antimicrobial Resistance at the Statens Serum Institute in Copenhagen. “Antibiotic resistance knows no bounds and can be transmitted between species.”
Researchers not involved in the study said the results helped confirm long-held assumptions about the dynamics of antibiotic resistance. Antimicrobials are abundant in nature, after all, and bacteria and fungi have long found ways to outsmart these compounds.
Lance Price, who directs the Antibiotic Resistance Action Center at George Washington University, praised 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 the most important thing about this paper is that 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 farm animal-associated MRSA, said the study helped highlight the role animals played as reservoirs for antimicrobial resistance. “It really just adds to the need for better antibiotic management and awareness of what we use in both human and veterinary medicine,” she said.
The MRSA that infected the hedgehogs did not seem to affect them, but its overwhelming presence in the animals removed from Denmark was largely similar to that of mecC.-MRSA prevalence among people in this country. First discovered in 2011, mecC.-MRSA has since spread to dairy herds across Northern Europe and can sometimes cause infections in cows, but has rarely made people sick.
Jesper Larsen, another lead author of the paper and a senior researcher at the Statens Serum Institute, said the results had already inspired him and other researchers to broaden their focus on antibiotic resistance in wildlife. However, he warned before any notion that naturally occurring resistance would somehow reduce the urgency to curb the use of antimicrobial drugs to treat diseases in humans.
“The lesson here is that by overusing antibiotics we are speeding up what is already happening in nature,” he said.
There may be more lessons to be learned from the study, added Dr. Larsen added. Although the risk of hedgehogs directly infecting humans with MRSA is likely to be minimal, it has always been advisable to keep a healthy distance from the animals.