The aggressive antibiotic-resistant staph infection responsible for thousands of recent illnesses undermines the body's defenses by causing germ-fighting cells to explode, researchers have reported. Experts say the findings may help lead to better treatments.

An estimated 90,000 people in the United States fall ill each year from methicillin-resistant Staphylococcus aureus, or MRSA. It is not clear how many die from the infection - one estimate put it at more than 18,000, which would be slightly higher than the US deaths from AIDS.

The infection long has been associated with health care facilities where it attacks people with reduced immune systems. But many recent cases involve an aggressive strain, community-associated MRSA, or CA-MRSA. It can cause severe infections and even death in otherwise healthy people outside of health care settings.

The CA-MRSA strain secretes a kind of peptide - a compound formed by amino acids - that causes immune cells called neutrophils to burst, eliminating a main defense against infection, according to researchers.

The findings, from a team of US and German researchers led by Michael Otto of the National Institute of Allergy and Infectious Diseases (NIAID), appeared in Sunday's online edition of the journal Nature Medicine.

While only 14 percent of serious MRSA infections are the community associated kind, they have drawn attention in recent months with a spate of reports in schools, including the death of a 17-year-old Virginia high school student.

The compounds first cause inflammation, drawing the immune cells to the site of the infection, and then destroy those cells.

The research was conducted in mice and with human blood in laboratory tests.

Within five minutes of exposure to the peptides from CA-MRSA, human neutrophils showed flattening and signs of damage. After 60 minutes, many cells had disintegrated completely.

"This elegant work helps reveal the complex strategy that S. aureus has developed to evade our normal immune defenses," Dr. Anthony S. Fauci, NIAID director, said.

(Agencies via Shanghai Daily November 13, 2007)