University of Iowa researchers have discovered what causes the lethal effects of staphylococcal infective endocarditis, a serious bacterial infection of heart valves that kills approximately 20,000 Americans annually. According to the UI study, the culprits are superantigens—toxins produced in large quantities by Staphylococcus aureus (staph) bacteria—which disrupt the immune system.
“The function of a superantigen is to 'mess' with the immune system,” says Patrick Schlievert, PhD, chair of microbiology at the UI Carver College of Medicine. “Our study shows that in endocarditis, a superantigen is over-activating the immune system, and the excessive immune response is contributing very significantly to the destructive aspects of the disease, including capillary leakage, low blood pressure, shock, fever, destruction of the heart valves, and strokes that may occur in half of patients.”
In the study, the UI scientists used a strain of methicillin resistant staph aureus (MRSA), which is a common cause of endocarditis in humans. They also tested versions of the bacteria that are unable to produce superantigens. By comparing the outcomes in the animal model of infection with these various bacteria, they proved that the lethal effects of endocarditis and sepsis are caused by the large quantities of the superantigen staphylococcal enterotoxin C (SEC) produced by the staph bacteria.
Published in the journal mBio, suggests that blocking the action of superantigens, either via therapeutics or vaccination, might provide a new approach for treating infective endocarditis. Read the study.
