Bacteria found in and out of U.S. hospitals produce a toxin that can kill pneumonia patients within 72 hours, researchers have found.

Staphylococcus aureus bacteria, or S. aureus, seem to be trading the gene for the toxin more often, Gabriela Bowden of the Texas A&M Health Science Center in Houston and her colleagues said in Thursday's online issue of the journal Science.

"If the community-acquired strain establishes itself in the hospital setting, it will be difficult to contain," Bowden said.

The community-associated strain of methicillin-resistant Staph, or CA-MRSA, produces a toxin called Panton Valentine leukocidin, or PVL.

Normally, staph are found in the nose or on the skin of about 25 to 30 per cent of people. They cause minor skin infections such as pimples and boils, as well as diseases such as meningitis, toxic shock syndrome and pneumonia.

In the study, researchers used mice to study the toxin produced by bacteria from current outbreaks of CA-MRSA and necrotizing pneumonia.

CA-MRSA causes serious skin and soft tissue infections in healthy persons who have not been recently hospitalized.

Necrotizing pneumonia destroys healthy lung tissue and can be fatal within 72 hours. Bacteria producing the PVL toxin also attack infection-fighting white blood cells, the researchers said. The necrotizing type killed two people in a British hospital in December.

"PVL is strong enough on its own to destroy the lungs," Dr. Marina Morgan, consultant medical microbiologist at Exeter Nuffield Hospital in Britain, said in a statement.

"The reason most patients die is that despite killing the bug, PVL toxins already formed continue to digest lung tissue, so we desperately need some way of removing the toxins."

People infected with the toxin-producing strain quickly develop a high fever that doctors should look out for, Bowden said. Handwashing is the best line of defence.