The bacterium Staphylococcus is known for its ability to develop resistance to most classes of antibiotics soon after they enter widespread clinical use. Vancomycin--a so-called last-ditch drug--can stop many of these multidrug-resistant strains. But some bacteria that are closely related to S. aureus--which often causes life-threatening infections in hospital settings--can fend off vancomycin, prompting concerns that soon S. aureus will, too. Scientists describe one instance of a vancomycin-resistant strain of the ubiquitous bug in the current issue of the journal Science and show that the gene responsible for its invulnerability jumped from another bacteria.

In June 2002, the vancomycin-resistant staph was cultured from foot ulcers on a patient in a Michigan hospital; fortunately, it did not spread throughout the clinic. Linda M. Weigel of the Centers for Disease Control and Prevention and her colleagues analyzed the microbe to determine the source of its resistance. They found that the responsible gene, Tn1546 (vanA), had come from another species of bug present in the patient's sore. According to the report, a circular, double-stranded unit of DNA known as a plasmid jumped from Enterococcus faecalis to the S. aureus strain, thereby conferring the ability to fight vancomycin.

The researchers tested whether this staph strain could in turn pass on its resistance to other types of Staphylococcus and found that the trait was indeed transferable. The authors note that their findings reinforce "concerns of potential widespread resistance to one of the few classes of agents still active against multidrug-resistant S. aureus.

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