News | January 18, 2007

Staph Bug Causes New Pneumonia

Jan. 19, 2007 - A staph germ circulating in and out of hospitals produces a poison that can kill pneumonia patients within 72 hours, researchers said on Thursday.

Staphylococcus aureus bacteria — or S. aureus — can pass one another the gene for the toxin and are apparently swapping it more often, the researchers report in Friday's issue of the journal Science.

The toxin, called Panton Valentine leukocidin, or PVL, can itself cause pneumonia and can kill healthy tissue.

Luckily, people infected with the bacteria quickly develop a high fever and astute doctors can identify it, said Gabriela Bowden of the Texas A&M Health Science Center in Houston, who led the study.

"This is a scary situation. We are trying to put the word out and to educate people about it," Bowden said in a telephone interview.

S. aureus is the most common cause of hospital-acquired infections, and can cause inflammation of the heart, toxic-shock syndrome and meningitis.

A new strain called MRSA resists the antibiotic methicillin, but it can be treated with antibiotics like doxycycline and vancomycin.

An outbreak of methicillin-resistant S. aureus carrying the new toxin killed two patients in a British hospital in December with a new type of pneumonia called necrotizing pneumonia. This infection destroys lung tissue and also kills some of the immune system cells sent to battle it.

Dr. Marina Morgan, consultant medical microbiologist at Exeter Nuffield Hospital in Britain, said the PVL toxin "turbo-charges" an already dangerous bacteria.

"PVL is strong enough on its own to destroy the lungs," she said in a statement.

And the toxin is immune to antibiotics.

"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," Morgan said.

S. aureus, which commonly live on the skin and cause pimples, boils and other minor infections, can cause a serious wound if the toxin-producing strains get into a cut.

Old-fashioned hygiene is the best line of defense, Bowden said.

"This is a community-associated strain, which means that in schools, the kids can carry it. Anybody can be colonized with it," she said.

"I tell my kids if you scrape your knee, go to the bathroom immediately and wash it with soap." Hospitals must impose strict hygiene to control it.

Bowden's team tested the PVL-producing Staph on mice and found that two days after infection, their lungs were filled with immune cells and lung tissue was starting to bleed and die.

A stretch of DNA known as a cassette carries the code for the PVL toxin. Such a little segment is easily passed from one strain of bacteria to another, said Bowden, and viruses called bacteriophages can also carry them.

Understanding how this happens could provide a way to develop new drugs or vaccines and shed light on how bacteria acquire new and dangerous qualities.

"The appearance of PVL toxin in severe Staphylococcal pneumonia is a recent phenomenon. Previously the toxin was only found in less than 5 percent of strains," said Dr. Ronald Cutler of the University of East London.

Some companies are working on staph vaccines but none is on the market.

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