Researchers at the Roslin Institute prove that MRSA type found in humans first developed in cattle more than 40 years ago.

Research has found that a type of MRSA found in humans originated in cattle at least 40 years ago.

Scientists at the Roslin Institute at the University of Edinburgh studied the genetic make-up of more than 40 strains of the bacterium Staphylococcus aureus, which can build up antibiotic resistance to develop into MRSA.

At least two genetic subtypes of the bacterium, which have become endemic in people, have been traced back to cattle. Research published in mBio concludes the most likely scenario is the bug crossed over from cattle to people through direct contact – perhaps through people working with farm animals.

After switching to human hosts, the Staphylococcus aureus bacterium became resistant to the antibiotic methicillin and developed into methicillin-resistant Staphylococcus aureus – or MRSA. According to the research, the bacteria acquired the ability to avoid attack by the human immune system.

However, these bacteria that originated in cattle do not appear to be more aggressive or more resistant to antibiotics than other MRSA affecting humans.

Lead researcher, Professor Ross Fitzgerald, of The Roslin Institute, said: “Human infections caused by bacteria being transmitted directly from livestock are well known to occur.

“However, this is the first clear genetic evidence of subtypes of S aureus that jumped from cattle and developed the capacity to transmit widely among human populations.”

Laura Spoor, of The Roslin Institute and first author on the research paper, added: “This research provides insight into how some strains of MRSA have evolved and help us better understand how they have adapted to cause disease in different host species.”

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