Beneath the spiny spines of European hedgehogs, a microbial deadlock may have spawned a dangerous drug-resistant pathogen long before the era of antibiotic use in humans.
There’s no question that antibiotic use accelerates drug-resistance in bacteria that colonize humans, says Jesper Larsson, a veterinarian at the Statens Serum Institute in Copenhagen. But, he says, these microbes had to get genes to confer resistance from somewhere, and scientists don’t know where most of these genes come from.
Now, for a type of methicillin-resistant Staphylococcus aureus, or MRSA, Larsen and his colleagues track its evolution to the hedgehog hundreds of years ago. On the skin of these critters, a fungus that produces natural antibiotics may have created an environment for the bacteria to develop drug resistance, researchers report Jan. Nature,
One of the most common drug-resistant pathogens, MRSA infects hundreds of thousands of people worldwide each year, and these infections can be difficult to treat. The specific type of MRSA on which the new study is focused causes a fraction of cases in humans.
The team first detected MRSA in hedgehogs by chance years ago when biologist Sophie Rasmussen, who was part of the new work and is now at the University of Oxford, contacted Larsen’s team about a sample of a freezer filled with dead hedgehogs. Of these animals collected from Denmark, 61 percent carried MRSA. “We found this extremely high prevalence in hedgehogs,” says Larsen, suggesting that the animals were a reservoir for drug-resistant superbugs.
In new work, scientists survey hedgehogs (erinaceus europaeus And erinaceus romanicus) from 10 European countries and New Zealand. Workers from wildlife rescue centers cleaned the nose, skin and feet of 276 animals. MRSA was prevalent in hedgehogs in the United Kingdom, Scandinavia and the Czech Republic.
to analyze s. aureusThe team found 16 strains of MECC-MRSA, named after genes that confer resistance, and mapped the evolutionary relationships between them by comparing mutations in their genetic instruction manuals, or genomes. From the analysis, the team inferred that the three oldest lineages emerged in hedgehog populations between 130 and 200 years ago, periodically infecting people and cattle, long before penicillin hit the market in the 1940s. Was. According to the researchers’ report, hedgehogs may be the source of nine out of 16 lineages.
“There is no doubt that the use of antibiotics is the main driver of resistance in human pathogens,” says Anders Larsson, a microbiologist at the Statens Serum Institute. Was also part of the team. “This is a very special case where we can track it back to the origins.”
But that doesn’t explain how elephants’ s. aureus developed resistance. The team got a clue about this from a research study from the 1960s Trichophyton erinacei, A fungus that causes “hedgehog ringworm” in humans. that study reported that T. erinacei Some were killed on the skin of an elephant s. aureus But not others who were resistant to penicillin. Increasing T. erinacei In the lab, the researchers identified two penicillin-like antibiotics pumped out by the fungus.
This finding suggests that hedgehogs are a MRSA reservoir because “they live in cheek by jowls with organisms that are producing penicillin,” says biochemist Gerry Wright of McMaster University in Hamilton, Canada, who was involved in the study. were not.
The fungus “lives in a bad neighborhood,” Wright says. They have to compete with other microbes, such as s. aureusfor resources and to colonize the host, and “they have to work on this arrangement where they can defend themselves.”
You can’t think of antibiotic resistance without considering the environmental connection, says Wright. They state that the evolution of resistance is a gradual process shaped by natural selection. Wright’s work has shown that in sites that have survived human impact, the origins of antibiotic resistance are ancient. People have mostly traced this evolution to the soil microbial community, or microbiome (SN: 2/14/06) but animal microorganisms provide another potential source for genes that confer resistance as well as sources for new antibiotics, he says.
The history of antibiotics over the past century has been a cycle of new drug discoveries, which are soon followed by increased microbial resistance to those drugs. This shouldn’t be a surprise, Wright says. “Because antibiotics have been on the planet for billions of years, and resistance is billions of years old,” he says. If scientists don’t better understand where resistance comes from, even as researchers discover new drugs, he says, we’re just playing catch-up.