Human MRSA strain 'originated in livestock'

Cattle The study suggests livestock was the original source of an MRSA strain now in people

A type of MRSA found in humans originated in cattle at least 40 years ago, new research has claimed.

Edinburgh researchers said they had "clear evidence" that livestock was the original source of an MRSA strain now widespread in people.

They studied the genetic make-up of 40 strains of a bacterium, Staphylococcus aureus, that can build up antibiotic resistance to develop into MRSA.

The Roslin Institute at Edinburgh University carried out the research.

At least two genetic subtypes of the bacterium, which have become endemic in people, were traced back to cattle by the scientists.

Immune system

They said the most likely scenario was the bug crossed over from cattle to people through direct contact - perhaps through people working with farm animals.

It is hoped the research will help scientists find out how bacteria is able to spread and cause disease in humans, and to prevent further strains from jumping from livestock.

After switching to human hosts, the Staphylococcus aureus bacterium became resistant to the antibiotic methicillin and developed into methicillin-resistant Staphylococcus aureus or MRSA.

The bacteria also acquired the ability to avoid attack by the human immune system.

However, the bacteria that originated in cattle did not appear to be more aggressive or more resistant to antibiotics than other MRSA affecting humans, researchers said.

Professor Ross Fitzgerald, Roslin Institute researcher, 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 Staph. aureus which jumped from cattle and developed the capacity to transmit widely among human populations."

The study has been published in the journal mBio.

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