Aggressive staph germ found to secrete compound that attacks immune cells

WASHINGTON – 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 reported Sunday. Experts say the findings may help lead to \nbetter treatments.\nAn 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 U.S. deaths from AIDS.\nThe 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.\nThe 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.\nThe findings, from a team of U.S. and German researchers led by Michael Otto of the National Institute of Allergy and Infectious Diseases, appeared in Sunday’s online edition of the journal Nature Medicine.\nWhile 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.\nBoth hospital-associated and community-associated MRSA contain genes for the peptides. But their production is much higher in the CA-MRSA, the researchers said.\nThe compounds first cause inflammation, drawing the immune cells to the site of the infection, and then destroy \nthose cells.\nThe research was conducted in mice and with human blood in laboratory tests.\nWithin five minutes of exposure to the peptides from CA-MRSA, human neutrophils showed signs of damage to their membrane, researchers said. After 60 minutes, many cells had disintegrated completely.\n“This elegant work helps reveal the complex strategy that S. aureus has developed to evade our normal immune defenses,” Dr. Anthony S. Fauci, the Institute’s director, said in a statement. “Understanding what makes the infections caused by these new strains so severe and developing new drugs to treat them are urgent public health priorities.”\nDr. Lindsey N. Shaw of the division of cell biology, microbiology and molecular biology at the University of South Florida, also was enthusiastic about the research.\n“Specifically identifying a factor which seemingly makes CA-MRSA more pathogenic than HA-MRSA is a real find,” Shaw, who was not part of the research group, said via e-mail. The “molecules identified in the study are indeed novel.”\nThe research was funded by the National Institutes of Health, the German Research Council and the German Ministry of Education and Research.