"The bacterial protein, called H-NS, is a very important molecule and affects the way a bacterial pathogen operates. By bringing in its own supply of the H-NS-like stealth protein (called Sfh), the plasmid avoids interfering with the natural balance of H-NS and DNA in the cell," explained Professor Dorman.

"Our work suggests that bacterial fitness can be manipulated by altering the proportions of H-NS and DNA in the cell, perhaps through the use of drugs, an insight that may be exploited in the future to prevent or to fight infection."

Bringing its own supply of the host-like protein is clearly an advantage for the plasmid, suggesting that the normal supply of H-NS in the bacterium may become limited when new DNA is imported. If a modified plasmid, lacking the sfh gene, is transferred to Salmonella, the effects of the plasmid are very rapidly detected.

Bacteria can acquire and transfer resistance genes through a variety of methods, but this new study shows how a single gene has the potential to increase dramatically the chance of successful - and health-threatening - transfer and survival of a battery of antibiotic-resistance genes.

The consequences for managing disease - especially in developing countries - are significant, explained Dr John Wain: "These plasmids are found in many pathogenic bacteria including those that cause typhoid and paratyphoid fever. Both of these diseases are increasing in the developing world and in the UK we are seeing more and more imported cases.

"But understanding is not enough: we now need to exploit this information to try to prevent the plasmid spreading any further."

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Contact: Don Powell
don@sanger.ac.uk
44-012-234-94956
Wellcome Trust Sanger Institute
11-Jan-2007