Infective endocarditis (IE) is an infection of a heart valve or the inner lining of the heart. The infection can damage or destroy the heart valves and thus dramatically impair heart function. Endocarditis usually occurs in patients with congenital or acquired heart conditions. Several different organisms can cause endocarditis but it is usually caused by bacteria and more than 80% of all cases are caused by Staphylococcus aureus and methicillin resistant Staphylococcus aureus (MRSA). In most cases, the infection develops when normal bacteria on the skin or in the respiratory, gastrointestinal, or urinary tract enter the bloodstream and lodge within a damaged heart valve or abnormal heart tissue.
The characteristic lesion in IE, the vegetation, is composed mainly of micro-organisms, inflammatory cells, fibrin and platelets.  Untreated, this bacterial infection rapidly damages the endocardium and causes the heart valve to malfunction and subsequently the patient to die. The main treatment for IE is broad spectrum antibiotic therapy and surgical valve repair. However, due to increasing antibiotic resistance and thereby greater likelihood of treatment failure and relapse rates as high as 15% the antibiotic therapy must be increasingly aggressive.