On the move.
MRSA bacteria are on the rise outside the hospital.
K. Lounatmaa / Photo Researchers Inc.
Mention resistant staph bacteria, and most people think about the almost invincible strains - formally called methicillin-resistant Staphylococcus aureus (MRSA) --What infect immunocompromised individuals and patients in hospitals. But in recent years, MRSA strains that are more virulent began to spread outside hospitals and attack people in perfect health ( Science , 14 March 03, p. 1639) . Now, researchers say they have discovered how these bugs, which some see as a major threat to public health, do their damage.
Typically transmitted in prisons, schools and locker rooms, "community associated" MRSA (CA -MRSA) can cause serious infections of the skin and soft tissue, pneumonia and an infection of the blood known the bacteremia name, sometimes with fatal consequences. Why bacteria are so virulent is uncertain. Many believe it is because all CA-MRSA strains carry the gene for a toxin called (PVL) Panton-Valentine; A recent Science document suggests that this molecule plays an important role in CA-MRSA caused by pneumonia ( Science , 23 February, p. 1130).
But some scientists disagree. "We fight about PVL much," said Michael Otto, a researcher at the Rocky Mountain Laboratories, part of the National Institute of Allergy and Infectious Diseases in Hamilton, Montana. He was not convinced by the Science paper, and points out that pneumonia occurs in about 2% of CA-MRSA. PVL does not appear to play a role in skin infections and soft tissue or bacteremia, said Otto.
Now his team found another group of biochemical guilty. They found that CA-MRSA strains produce called phenol-soluble modulins peptides (PSM) in much larger quantities than do strains . hospital When the researchers knocked the genes for four of these peptides, the so-called PSMs of α-type, CA-MRSA bacteria have become much softer in mice: skin infections were less severe, and bacteremia was less often fatal. Apparently, the peptides are the most virulent microbe, the authors concluded
Learn why PSM-aS are destructive, the researchers added the peptides in human neutrophils -. A class of white blood cell that engulfs the bacteria --In the test tube. Neutrophils have started to collapse within 5 minutes, and less than an hour, many have been completely destroyed. So PSMs seem to strike a defense system, said Otto, giving vent MRSA.
"I have no doubt that these peptides contribute to the virulence of Staphylococcus aureus ," said Francois Vandenesch the University of Lyon in France, which has long defended the hypothesis and PVL co-author of science paper.. But he still believes PVL plays a major role as well
Henry Chambers, who is studying MRSA at the University of California, San Francisco, said PSMs that form "an attractive alternative explanation" for PVL - but both can be important. If the results of Otto maintain, Chambers said, they offer researchers a series of new drug targets.
Related site
- More CA-MRSA, the Centers for Disease Control and Prevention
0 Komentar