Scientists have found evidence that a type of antibiotic-resistant MRSA superbug appeared in nature long before the use of antibiotics in humans and livestock, which has traditionally been blamed for its emergence.
The hedgehogs carry a fungus and bacteria on their skin, and the two are locked in a battle for survival. The fungus secretes antibiotics to kill the bacteria, but in response the bacteria developed resistance to the antibiotics – becoming resistant to methicillin Staphylococcus aureus, or MRSA. Up to 60% of hedgehogs carry a type of MRSA called DudeC-MRSA, which causes 1 in 200 of all MRSA infections in humans. Natural biological processes, not the use of antibiotics, led to the initial emergence of this superbug on hedgehogs around 200 years ago.
Staphylococcus aureus first developed resistance to the antibiotic methicillin around 200 years ago, according to a large international collaboration including the University of Cambridge, the Wellcome Sanger Institute, Denmark’s Serum Statens Institute and the Royal Botanic Gardens, Kew , which traced the genetic history of the bacterium.
They were investigating the startling finding – from surveys of hedgehogs in Denmark and Sweden – that up to 60% of hedgehogs carry a type of MRSA called DudeC-MRSA. The new study also found high levels of MRSA in swabs taken from hedgehogs across their range in Europe and New Zealand.
The study is published today in the journal Nature.
Researchers believe that antibiotic resistance evolved in Staphylococcus aureus as an adaptation to having to exist side by side on the hedgehogs skin with the fungus Trichophyton erinaceiwhich produces its own antibiotics.
The resulting methicillin resistance Staphylococcus aureus is better known as the MRSA superbug. The discovery of this age-old antibiotic resistance predates the use of antibiotics in medical and agricultural settings.
“Thanks to sequencing technology, we have found the genes that give DudeC-MRSA has had its resistance to antibiotics since it first emerged and was discovered to exist in the 19th century,” said Dr Ewan Harrison, researcher at the Wellcome Sanger Institute and University of Cambridge and lead author of the study .
He added: “Our study suggests that it was not the use of penicillin that led to the initial emergence of MRSA, it was a natural biological process. We believe that MRSA evolved in a battle for surviving on the skin of hedgehogs, and then spread to livestock and humans through direct contact.”
Antibiotic resistance in insects causing human infections was previously thought to be a modern phenomenon, driven by the clinical use of antibiotics. The overuse of antibiotics is now accelerating the process and antibiotic resistance is reaching dangerously high levels in all parts of the world.
Since nearly all the antibiotics we use today are naturally occurring, researchers say it’s likely that resistance to them already exists in nature as well. Overuse of any antibiotic in humans or livestock will promote resistant strains of the insect, so it is only a matter of time before the antibiotic begins to lose its effectiveness.
“This study is a clear warning that when we use antibiotics, we must use them with care. There is a very large ‘reservoir’ of wild animals where antibiotic-resistant bacteria can survive – and from there, there is no It’s just a short step from them being picked up by livestock and then infecting humans,” said Professor Mark Holmes, a researcher at Cambridge University’s Department of Veterinary Medicine and lead author of the report.
In 2011, earlier work led by Professor Holmes first identified DudeC -MRSA in human and dairy cow populations. At the time, it was believed that the strain originated in cows due to the large amount of antibiotics they were regularly given.
MRSA was first identified in patients in 1960, and approximately 1 in 200 MRSA infections are caused by DudeC-MRSA. Due to its resistance to antibiotics, MRSA is much more difficult to treat than other bacterial infections. The World Health Organization now considers MRSA to be one of the greatest global threats to human health. It is also a major issue in breeding.
Findings are no reason to fear hedgehogs, researchers say: Humans rarely contract infections with DudeC-MRSA, even though it has been present in hedgehogs for over 200 years.
“It’s not just hedgehogs that harbor antibiotic-resistant bacteria — all wild animals carry many types of bacteria, as well as parasites, fungi and viruses,” Holmes said.
He added: “Wild animals, livestock and humans are all interconnected: we all share an ecosystem. It is not possible to understand the evolution of antibiotic resistance unless we look at the whole system.