Emerging S aureus strains adept at avoiding the immune system

Community-acquired Staphylococcus aureus is deadlier and better at evading human immune defenses than strains of S aureus that originate in health-care settings, assert the authors of a recent article in the Journal of Immunology.

Scientists from the National Institute of Allergy and Infections Diseases (NIAID) Rocky Mountain Laboratories (RML) came to this conclusion when they studied how the immune system reacts to strains of S aureus bacteria by examining the ability of methicillin-resistant strains to cause disease in mice and avoid destruction by neutrophils.

The study identified specific S aureus genes that may control the bacterium's escape from the grasp of neutrophils. Among thousands of S aureus genes analyzed in the five different strains used in the study, the researchers identified a large group whose role in helping spread the infection was previously unknown.

"The reason that some mild infections become severe or fatal is not well understood, but virulence is often associated with certain strains," said the study's lead author, Jovanka Voyisch, PhD, of RML. "These results suggest that community-acquired methicillin-resistant S aureus causes disease in healthy people in part because it has enhanced ability to circumvent killing by neutrophils."