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MRSA arose naturally in hedgehogs long before antibiotics, Cambridge researchers show



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The rise of the superbug MRSA has typically been blamed on the overuse of antibiotics in humans and livestock - but it appears hedgehogs have been harbouring it for hundreds of years.

Scientists believe that antibiotic resistance evolved in Staphylococcus aureus as it adapted to existing side-by-side on the skin of hedgehogs with Trichophyton erinacei, a fungus that produces its own antibiotics.

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. Picture: Claire L Raisen (54157495)
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. Picture: Claire L Raisen (54157495)

The researchers at the University of Cambridge, the Wellcome Sanger Institute, Denmark’s Serum Statens Institut and the Royal Botanic Gardens, Kew, traced the genetic history of the bacteria to discover that natural biological processes drove the emergence of the superbug.

It follows hedgehog surveys from Denmark and Sweden that showed up to 60 per cent of hedgehogs carry a type of MRSA called mecC-MRSA.

The new study found high levels of MRSA in swabs from hedgehogs across Europe and New Zealand too.

Hedgehog (49643300)
Hedgehog (49643300)

Dr Ewan Harrison, a researcher at the Sanger Institute and University of Cambridge and a senior author of the study, published in Nature, said: “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.

“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.”

However, the findings are not a reason to fear hedgehogs, as humans rarely get infections with mecC-MRSA, even though it has been present in the animals for two centuries.

Overuse of antibiotics is accelerating the process of antibiotic resistance, which is now at dangerously high levels around the world.

MRSA spreads from hedgehogs to humans, either directly or via domestic animals. Illustration. Picture: Jesper Larsen (54157499)
MRSA spreads from hedgehogs to humans, either directly or via domestic animals. Illustration. Picture: Jesper Larsen (54157499)

And since almost the antibiotics we use today arose in nature, the scientists say it is likely that resistance to them already exists in nature too.

Prof Mark Holmes, a researcher in the University of Cambridge’s Department of Veterinary Medicine and a senior author of the report, said: “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.”

Prof Holmes first identified mecC -MRSA in human and dairy cow populations in 2011, when it was assumed it had arisen in cows because of the antibiotics they are given.

MRSA spreads from hedgehogs to humans, either directly or via domestic animals. Illustration. Picture: Jesper Larsen (54157501)
MRSA spreads from hedgehogs to humans, either directly or via domestic animals. Illustration. Picture: Jesper Larsen (54157501)

MRSA - now a major threat to human health and livestock farming - was first found in patients in 1960, with about one in 200 of all MRSA infections are caused by mecC-MRSA.

”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,” said Prof 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.”

This research was funded by the Medical Research Council.

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