Antibiotic-resistant MRSA bacteria evolved in hedgehogs 200 years ago, genetic study finds


A type of methicillin resistant Staphylococcus aureus – MRSA, the antibiotic-resistant bacterial scourge of modern clinical medicine – may have evolved 200 years ago in European wild hedgehogs, according to a recent study.

As you read this, your body is teeming with bacteria. There’s about a 30% chance that your normal, healthy microbiome will include a thriving population of a bacterial species called Staphylococcus aureus either on your skin or in your nose. Most of the time, these small, round bacteria are just harmless, but they can turn deadly.

Even a small cut or break in the skin can leave S. aureus inside, where infection can cause blisters, boils, cellulitis or impetigo. It is also a common cause of food poisoning. In the bloodstream, S. aureus can hitchhike to vital organs; it can also infect bones, joints, and even the surfaces of medical implants. And it’s getting harder and harder for doctors to fight back.

Almost all S. aureus strains circulating today are resistant to penicillin, and about 60% are also resistant to methicillin – which is part of a class of antibiotics developed specifically to fight bacteria resistant to penicillin. Doctors began prescribing methicillin in 1959. MRSA appeared the following year.

Logically, all types of MRSA must have evolved in hospital patients as the next step in the ongoing arms race between humans and bacteria – or at least that’s what it seems for 60 years. A recent study, published in the journal Nature, suggests that at least one strain of S. aureus Methicillin resistance genes evolved at least 200 years ago on the skin of wild hedgehogs.

It is not a scene; It’s an arms race “

It all started, as most scientists do, with rigorous data collection – which in this case means biologists chased many wild hedgehogs in order to swab their skin with cotton swabs and look for germs. . About 60% of hedgehogs that waddle in Denmark and Sweden carry mecC-MRSA, a specific strain of methicillin resistance S. aureus. Biologist Evan Harrison and veterinary researcher Mark Holmes, both from the University of Cambridge, also found surprisingly high levels of MRSA in hedgehogs elsewhere in Europe, as well as in New Zealand.

S. aureus is a normal part of the microbiome for most hedgehogs, as it is for about 30% of people. On hedgehogs, however, the bacteria live alongside a fungus called Trichophyton erinacei. To protect against the bacteria, the fungus produces methicillin. To maintain a chance at fighting the fungus, the bacteria apparently evolved to resist methicillin.

This kind of evolving arms race is constantly going on in nature, and that’s normally a good thing for us. Most of the chemicals we use as antibiotics are borrowed from fungi and bacteria that try to defend themselves against their microbial rivals. In this case, however, the T. erinacei bacteria living on wild hedgehogs have succeeded in doing the same thing as the modern medical system: creating sufficient selective pressure on bacteria to develop resistance to antibiotics.

But the hedgehog microbiomes arrived about 200 years ago, according to Harrison, Holmes and their colleagues. They sequenced the DNA of mecC-MRSA they found on hedgehog skin and compared it to DNA from other strains. DNA accumulates tiny mutations over time, at a fairly constant rate. Geneticists can count these mutations to estimate how long it was last two organisms shared a common ancestor – in other words, they can estimate how long a particular strain of MRSA has been around.

“We tracked down the genes that have given mecC-MRSA its resistance to antibiotics since their first appearance and found that they existed on 19e century, ”said Harrison.

What is mec MRSA?

MRSA infections are difficult to treat because the bacteria can resist not only methicillin, but a whole class of similar antibiotics called β-lactam antibiotics. This stubborn resistance is the work of a gene called mecA. Regular, non-resistant S. aureus, a different gene produces a protein that binds to β-lactam antibiotics, giving them a chance to attach themselves to and destroy the bacteria. But in MRSA, mecA produces a protein that habit bind to lactam antibiotics. A S. aureus The bacteria with mecA is resistant to methicillin and its classmates because antibiotics literally can’t get the germ under control.

About 1 in 200 MRSA infections – that is, in humans – have a different version of this gene called mecC. It also produces a protein that does not bind to β-lactam antibiotics, but its genetic code is different from that of mecA. The two genes are homologous, meaning they share a common ancestor, but over time they have developed slightly different versions of antibiotic resistance.

Holmes and his team first discovered mecC-MRSA in humans and dairy cows in 2011. In 2014, it was present in 14 different species in 13 European countries. At the time, Holmes and others speculated that mecC-MRSA evolved in dairy cows because farmers routinely give their cattle huge doses of antibiotics to prevent infection. This practice is now discouraged as it creates a hotbed for the development of antibiotic resistance.

But the new study suggests mec-MRSA may have appeared in hedgehogs first, long before humans, or cows, took antibiotics.

“We believe MRSA evolved into a battle for survival on the skin of hedgehogs, and then spread to livestock and humans through direct contact,” Harrison said.

Please don’t lick the hedgehogs

“This study is a clear warning that when we use antibiotics, we need to use them with caution,” Holmes said. “There is a very large ‘reservoir’ of wild animals where antibiotic resistant bacteria can survive – and from there it is only a short step away from being picked up by livestock and then infecting humans. . “

Since nearly all of the antibiotics we use today – and probably most of the ones we will use in the future – have been found in nature, it is likely that resistance to these antibiotics also exists somewhere in nature. “It’s not just hedgehogs that harbor antibiotic-resistant bacteria,” Holmes said. “All wild animals carry many types of bacteria, as well as parasites, fungi and viruses. Besides, all humans too.

This is no reason to be afraid of hedgehogs. Today, only about 0.5% of human MRSA infections are of the mecC type, making it extremely rare, although it has been waddling for 200 years.

But as a precaution, avoid licking hedgehogs if possible; they are still very hot.


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