Researchers told the Federation of Infection Societies Conference at the University of Cardiff in Wales that new strains of methicillin resistant Staphylococcus-aureus, known as MRSA, are often characterized by the toxin Panton-Valentine leucocidin, or PVL, which kills white blood cells -- the body's key defense against invasive bacteria.

"Although the resistant strain is not yet widespread in the United Kingdom, we have seen increasing numbers of PVL- toxin producing Staphylococcus aureus infections, mainly presenting with recurrent boils and abscesses," Dr. Marina Morgan of the Royal Devon & Exeter Foundation National Health Service Trust said in a statement. "This excessive production of white cells to compensate for those killed by the PVL toxin leads to recurrent severe boils and abscesses."

A minority of patients carrying the PVL-producing staphylococci can suffer severe invasive infections such as septicaemia or a lethal form of pneumonia in which the lung tissue is destroyed by the toxin, Morgan said.