Page last updated at 19:16 GMT, Thursday, 21 January 2010

MRSA superbug strain 'tracked' via genome

The appearance of MRSA has been linked to widespread antibiotic use

Researchers have developed a technique for precisely tracking the spread of the superbug MRSA in hospitals.

The team from the Wellcome Trust Sanger Institute in Cambridge looked at the genomes of MRSA strains from across the globe and at one hospital in Thailand.

They were able to spot small changes that allowed them to track the strain back to an individual patient.

They say this adds to the understanding of how MRSA can spread so rapidly and should lead to better treatments.

DNA sequencing

The research, which is published in the journal Science, involved teams in the UK, in Bath, Oxford and London, and Thailand, Portugal and the United States.

Scientists used new high-throughput DNA sequencing technologies to compare MRSA samples from patients to show how they were genetically related.

This work is a great demonstration of new, rapid DNA sequencing that in the near future will be how important pathogens such as MRSA will be identified
Prof Mark Enright, Imperial College London

They were able to spot single-letter differences in the genetic code.

They looked at two different sets of samples: one set taken from people across the globe and another from a single hospital in Thailand.

They sequenced the entire genomes of each sample.

In the hospital setting it revealed single letter genetic changes in the samples showing that no two infections were caused by entirely identical bacteria.

This allowed them to discover whether one patient had infected another or whether the infection had come in from another source.

They found that the MRSA strain studied acquired about one single-letter change in its genetic code every six weeks.

Worldwide search

They also looked at samples from hospitals in several parts of the world collected over more than 20 years.

The rate of mutation apparently supports the theory that MRSA emerged in the 1960s at the time of widespread antibiotic use.

Professor Sharon Peacock, a microbiologist at the University of Cambridge said: "The implications for public health are clear. This technology represents the potential to trace transmission pathways of MRSA more definitively so that interventions or treatments can be targeted with precision and according to need."

Researchers say it would be too expensive to use the technology widely at present but the cost should fall in the next few years.

Professor Mark Enright, an expert in molecular epidemiology at Imperial College, London, said the work gave researchers "a good idea as to how this particular type of MRSA has evolved and how it behaves in and out of hospitals".

"This work is a great demonstration of new, rapid DNA sequencing that in the near future will be how important pathogens such as MRSA will be identified," he said.

"Such unambiguous identification will form the basis for rapid diagnostics of microbial infection and will tell us how they spread in hospitals identifying each human host and surface in chains of transmission between patients."

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