Antibiotic use 'may have spawned MRSA'

Early use of antibiotics in the 1960s may have given birth to one of the most common strains of MRSA, a study has found.

A new genetic method of tracking infection suggests that the superbug emerged five decades ago in Europe, just as antibiotics were being widely introduced for the first time.

Scientists used DNA-mapping technology to compare the genetic relatedness of bugs isolated from individual patients.

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By identifying letter changes springing up in the bacteria's genetic code, they were able to track MRSA transmission between continents.

The technique, pioneered by scientists at the Wellcome Trust Sanger Institute in Cambridgeshire, is expected to help improve infection control strategies aimed at keeping superbugs at bay.

The scientists focused on 63 samples of MRSA – methicillin resistant staphylococcus aureus – from a particular lineage of the bacterium called ST239. The strain accounts for a large proportion of MRSA outbreaks in hospitals around the world.

Analysis of the samples yielded a "family tree" showing how ST239 had spread around the world and branched into clusters of sub-strains.

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The European samples were concentrated around the base of the evolutionary tree. Working backwards, the scientists established that the strain probably emerged in Europe in the 1960s.

The finding lends support to the theory that the widespread use of antibiotics in the 1960s may have spawned MRSA.

Another discovery was that one MRSA outbreak in a London hospital was probably due to a bacterial strain imported from south-east Asia – possibly brought in by a single infected patient.