Staph germ bursts immune cells, study says

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 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 U.S. 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 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.

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.

Both hospital-associated and community-associated MRSA contained genes for the peptides. But their production was much higher in the CA-MRSA, the researchers said.

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 to their membrane, researchers said. After an hour, many cells had disintegrated completely.

Dr. George G. Zhanel, a medical microbiologist at the University of Manitoba in Canada, said the study was the first he had seen that identifies the peptides involved.

This shows at least one of the reasons CA-MRSA is able to cause serious problems, Zhanel, who was not part of the research team, said in a telephone interview.

Findings like this may help lead to better treatments, such as ways to neutralize the peptides or to activate the immune system to defeat them, he added.

The research was funded by the National Institutes of Health, the German Research Council and the German Ministry of Education and Research.