Deadly Bacteria Times Its Attack

THURSDAY, July 28, 2005 (HealthDay News) -- Scientists have gleaned new insights in how the Pseudomonas aeruginosa bacterium -- a potentially lethal organism that's a frequent cause of infections after surgery -- gets past the human immune system's distress code.

Cracking the code, the bacteria recognizes the moment when a person is most vulnerable and times its attack to before the immune system can mount a strong defense, according to a study published in the July 29 issue of Science.

Researchers at the University of Chicago found the bacteria detect interferon-gamma, a chemical messenger used by the immune system to coordinate its attacks against invaders. The bacteria recognize interferon-gamma as a threat and then somehow assesse their own ranks. If they conclude their numbers are sufficiently large, the bacteria activate genes that turn them from harmless bowel dwellers into deadly invaders of the bloodstream.

"Most of the time these microbes are content to live and grow in our intestines," study director Dr. John Alverdy, a professor of surgery, said in a prepared statement.

This form of bacteria colonizes the intestines of about 3 percent of healthy people.

"They don't feel the need or even look for the opportunity to attack. But when they detect a threat, they have a remarkably sophisticated defense plan, based, unfortunately, on the notion that the best defense is an overwhelming offense," Alverdy said.

"Our goal is to understand the many steps in this process and use that knowledge to find novel ways to intervene, to stop the infection before it starts, rather than trying to kill all the germs," he said.

More information

The U.S. National Institute of Allergy and Infectious Diseases has more about microbes.