Piercing Staph Bug's 'Golden Armor'

Better understanding of this lethal bacterium points to weakness

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MONDAY, July 11, 2005 (HealthDay News) -- A biochemical shield of golden armor helps the Staphylococcus aureus bacterium thwart attacks by the human immune system, according to researchers at the University of California, San Diego School of Medicine.

The finding may help lead to new treatments for serious "Staph" infections that are becoming increasingly resistant to standard antibiotics. Staph is the leading cause of human infections in the skin and soft tissues, bones and joints, abscesses and normal heart valves.

The UCSD team found that the molecules that give Staph its golden color help protect the bacteria from being killed by neutrophils, white blood cells that play a leading role in immune system defense against invading microbes.

These molecules coating the surface of Staph are called carotenoids, similar to those found in carrots and other vegetables and fruit. The carotenoids inactivate deadly chemicals deployed by the immune system's neutrophils.

For their research, the investigators knocked out the genes in Staph that produce the carotenoid molecules. The result was a mutant strain of Staph that were white instead of the normal gold color.

"We found that the nonpigmented Staph mutant became much more susceptible to oxidants such as hydrogen peroxide and singlet oxygen produced by neutrophils. Without its golden pigment, the Staph lost its ability to survive in human neutrophils or blood, and could no longer form an abscess when injected into the skin of experimental mice," Dr. George Liu, research fellow in the UCSD department of pediatrics, said in a prepared statement.

The findings, published in the July 17 issue of The Journal of Experimental Medicine, suggest a new approach for treating serious Staph infections.

"Instead of attempting to kill the bacteria directly with standard antibiotics, a treatment strategy to inhibit the Staph pigment would disarm the pathogen, making it susceptible to clearance by our normal immune defenses," study senior author Dr. Victor Nizet, UCSD associate professor of pediatrics and an infectious disease specialist at Children's Hospital, San Diego, said in a prepared statement.

More information

The Nemours Foundation has more about Staph infections.

SOURCE: University of California, San Diego, news release, June 11, 2005

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