Staph Strains Increasingly Deadly

A study has found that antibiotic-resistant Staphylococcus aureus bacteria are more deadly and better at evading immune defenses than more common S aureus strains that originate in hospitals and other healthcare settings.

These antibiotic-resistant strains can sicken otherwise healthy people, resulting in community-acquired infections. Both S aureus and methicillin-resistant S aureus (MRSA) are increasing at an alarming rate and are difficult to treat, according to the new study, whose findings were reported in the September 7, 2005, online issue of the Journal of Immunology. The study was conducted by scientists at the U.S. National Institute of Allergy and Infectious Diseases (NIAID, Bethesda, MD, USA).

The scientists examined the ability of MRSA strains to cause disease in mice and avoid destruction by human white blood cells, or neutrophils, which make up about 60% of all white blood cells and are the first line of defense against bacteria. Although the scientists know the community-acquired strains differ from hospital strains, they do not know why the community strains cause more serious infection in otherwise healthy people.

In their study, the scientists identified specific S aureus genes that potentially control the bacterium's escape from neutrophils. Among thousands of S aureus genes analyzed, they identified a large group of genes whose role in helping spread infection is unknown. They are planning to determine if some of the unknown genes help promote disease. If they find which genes control S aureus to evade and destroy neutrophils, their work could lead to new medical treatments for bacterial infection.

"To cause human disease, bacterial pathogens must avoid being killed by neutrophils,” said Jovanka Voyich, Ph.D., of NIAID's Rocky Mountain Laboratories (RML) in Hamilton (MT), who directed the study. "These results suggest that community-acquired MRSA causes disease in healthy people in part because it has enhanced ability to circumvent killing by neutrophils.”




Related Links:
U.S. National Institute of Allergy and Infectious Diseases