Superbug MRSA arose in hedgehogs long before it cropped up in hospitals

The rise of antibiotic-resistant bacteria has been labelled one the biggest current threats to global health, food security, and development. This resistance has long been thought to be a modern phenomenon, driven by the clinical use of antibiotics, with widespread overuse accelerating the process.

New research, published today in the journal Nature, reveals that this isn’t a modern phenomenon, and is in fact an evolutionary arms race that has been quietly raging for centuries – on the skin of the humble hedgehog.

The study, an international collaboration including the University of Cambridge, the Wellcome Sanger Institute, Denmark’s Serum Statens Institut and the Royal Botanic Gardens, Kew, traced the genetic history of Staphylococcus aureus (golden staph) – a bacterium notorious for its antibiotic resistant ‘superbug’ form. Though generally harmless when present on the surface of our skin, staph can be problematic if it manages to get inside the body, often through cuts.

Since the first detection of a Methicillin-resistant form of this bacterium (MRSA) in 1961, the list of antibiotics that staph can resist has ballooned. Researchers developing new antibiotics are struggling to keep up.

But they’re not alone in the fight: Trichophyton erinacei, a fungus that lives on the skin of hedgehogs, has been waging war against MRSA for 200 years.

Living side-by-side with staph, which also calls hedgehogs home, T. erinacei produces its own antibiotics in the battle for hedgehog real estate. Researchers have now shown that the highly adaptable staph bacterium first developed antibiotic resistance in response to this fungal assault around 200 years ago, predating the introduction of antibiotics in medical and agricultural settings.

Photo shows fungus trichophyton erinacei growing in the centre of an agar plate streaked with mrsa on the left half and methicillin-susceptible staphylococcus aureus bacteria on the right.
Photo shows fungus Trichophyton erinacei growing in the centre of an agar plate streaked with MRSA on the left half and methicillin-susceptible Staphylococcus aureus bacteria on the right. The fungus produces antibiotics, which kill methicillin-susceptible Staphylococcus aureus bacteria but not MRSA, resulting in a clear zone on the right with no bacterial growth. Credit: Claire L. Raisen

The researchers came across this while investigating the surprising discovery – from hedgehog surveys from Denmark and Sweden – that up to 60% of hedgehogs carry a type of MRSA called mecC-MRSA. The current study also found high levels of MRSA in swabs taken from hedgehogs across their range in Europe and New Zealand.

“Using sequencing technology we have traced the genes that give mecC-MRSA its antibiotic resistance all the way back to their first appearance, and found they were around in the nineteenth century,” says Dr Ewan Harrison, a senior author of the study.

“Our study suggests that it wasn’t the use of penicillin that drove the initial emergence of MRSA, it was a natural biological process. We think MRSA evolved in a battle for survival on the skin of hedgehogs, and subsequently spread to livestock and humans through direct contact.”

The findings are not a reason to fear hedgehogs, say the researchers: humans rarely get infections with mecC-MRSA, even though it has been present in hedgehogs for more than 200 years. It is estimated that only around 1 in 200 of all MRSA infections are caused by mecC-MRSA.

Instead, they call attention to greater danger of antibiotic misuse.

“This study is a stark warning that when we use antibiotics, we have to use them with care. There’s a very big wildlife ‘reservoir’ where antibiotic-resistant bacteria can survive – and from there it’s a short step for them to be picked up by livestock, and then to infect humans,” says Professor Mark Holmes, a researcher in the University of Cambridge’s Department of Veterinary Medicine and a senior author of the report.

“It isn’t just hedgehogs that harbour antibiotic-resistant bacteria – all wildlife carries many different types of bacteria, as well as parasites, fungi and viruses,” says Holmes.

“Wild animals, livestock and humans are all interconnected: we all share one ecosystem. It isn’t possible to understand the evolution of antibiotic resistance unless you look at the whole system.”

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