MRSA (methicillin-resistant Staphylococcus aureus) is a dangerous antibiotic-resistant superbug often found infecting vulnerable hospital patients. Commonly thought to have emerged in the mid-20th century as a result of excessive antibiotic use, a new study is presenting evidence to suggest a particular strain of MRSA actually first appeared naturally up to 200 years ago in hedgehogs.
MRSA was first detected in the early 1960s. Its emergence came just a few years after the introduction of the then new antibiotic methicillin. Many researchers often cite MRSA as a good example of how quickly pathogenic bacteria can develop resistance to antibiotics.
Over the past 20 years researchers have been able to genetically identify several different strains of MRSA. One particular strain, dubbed mecC-MRSA, was detected in livestock populations in 2011. Again, it was suspected antibiotic use, this time in agriculture, may have contributed to its emergence, resulting in a zoonotic leap to humans.
More recently, however, studies of hedgehogs in Sweden and Denmark revealed the presence of mecC-MRSA in most of the animals. These curious discoveries led a team of international researchers to wonder whether this strain of MRSA arose in hedgehogs through natural selection.
“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 Ewan Harrison, a senior author on 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 hypothesis raised by the intriguing new study is that this strain of antibiotic-resistant bacteria evolved as a response to a fungus that lives on the skin of hedgehogs called Trichophyton erinacei. This fungus has been shown to produce a penicillin-like substance so it is suggested Staphylococcus aureus evolved the ability to resist that antibiotic-like molecule, enabling the fungus and bacteria to co-exist in hedgehogs.
Although mecC-MRSA is thought to account for less than one percent of human MRSA infections, the researchers behind this new study say it is possible plenty of currently problematic antibiotic-resistant bacteria could have emerged in nature. Mark Holmes, a senior author on the new study, says the vast majority of antibiotics we currently use come from natural sources so it is plausible to suggest there are bacteria out there with natural resistance.
“This study is a stark warning that when we use antibiotics, we have to use them with care,” says Holmes. “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.”
The researchers suspect transmission of mecC-MRSA directly from hedgehogs to humans is unlikely. It is more probable zoonotic transmission occurred through secondary animals such as cows.
And Holmes points out the study should not be a reason to worry about exposure to hedgehogs. After all, the findings suggest mecC-MRSA has been widespread in the animals for 200 years and human infections are still relatively rare.
The biggest takeaway from these findings, according to Holmes, is the reminder than a massive variety of undiscovered pathogenic organisms are carried by wildlife. And the study of antibiotic-resistant bacteria in particular should increasingly pay attention to the potential for animals to carry new and dangerous organisms.
”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,” adds 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 new study was published in the journal Nature.
Source: University of Cambridge