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"Superbug" arose in hedgehogs long before antibiotics

Antibiotics have been mass produced since the 1940s and have been used widely to treat infections caused by bacteria. Although their use has resulted in vastly improved health outcomes for millions of people, antibiotic resistance in bacteria has become a serious public health problem. The accepted understanding is that resistance in human pathogens is a modern phenomenon that is driven by the clinical use (or over prescription) of antibiotics. 

Bacteria may become resistant to antibiotic treatments when the medication is used unnecessarily (for example, to treat a viral infection – antibiotics do not kill viruses), or when patients do not complete a course of antibiotics. This has the effect of leaving the most resistant of bacterial cells behind, able to divide and form new cells that are also resistant. Once resistant to a common antibiotic, treatment with a new, more powerful antibiotic must commence if the infection is to be stopped.

In a study published today in the journal Nature, an international team of scientists has found that antibiotic resistant bacteria exist on hedgehogs and that this resistance first developed around 200 years ago, long before the use of antibiotics commenced. 

The scientific team, including researchers from the University of Cambridge, the Wellcome Sanger Institute, Denmark’s Serum Statens Institut and the Royal Botanic Gardens, Kew, present evidence that a type of antibiotic resistant Staphylococcus aureus is found commonly on hedgehog skins and that it arose in nature long before the use of antibiotics in humans and livestock.

In many healthy hedgehogs, the bacterium Staphylococcus aureus is found on the skin between the quills. In addition, hedgehog skin is home to a species of fungus, Trichophyton erinaceid, and the two types of organisms compete for space. The fungus secretes a type of antibiotic that controls the presence of the bacterium and, over time, this has led to the development of antibiotic resistant S. aureus on the skins of many hedgehogs. This pathogen is now known as methicillin-resistant S. aureus, or MRSA.

Unfortunately, MRSA infects people as well. Up to 60 percent of hedgehogs examined in the study carried a type of MRSA called mecC-MRSA, which causes 1 in 200 of all MRSA infections in humans. Analysis of the genetic changes that occurred in the genome of mecC-MRSA show that this pathogen emerged around 200 years ago and therefore natural, biological processes drove its evolution, not antibiotic use. 

“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,” said Dr. Ewan Harrison, a researcher at the Wellcome Sanger Institute and University of Cambridge.

“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.”

Antibiotic resistance in pathogens that cause human infections has commonly been thought of as a modern phenomenon, caused by clinical use of antibiotics. However, misuse of antibiotics is now accelerating the process, and antibiotic resistance is rising to dangerously high levels in all parts of the world. 

MRSA was first identified in patients in 1960, but today the World Health Organization considers MRSA to be one of the world’s greatest threats to human health. It is also a major challenge in livestock farming. Because of its resistance to antibiotics, MRSA is more difficult to treat and has gained the reputation of being a ‘superbug’ that colonizes hospitals, nursing homes and other health care facilities. 

Since almost all the antibiotics we use today arose in nature, the researchers say it is likely that resistance to them already exists in nature too. Overuse of any antibiotic in humans or livestock will favor resistant strains of the pathogen, so it is only a matter of time before the antibiotic starts to lose its effectiveness.

“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,” said Professor Mark Holmes, a researcher in the University of Cambridge’s Department of Veterinary Medicine.

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

The researchers stress that the findings should not make people fear hedgehogs: humans rarely get infections with mecC-MRSA, even though it has been present in hedgehogs for more than 200 years.

By Alison Bosman, Staff Writer

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