What causes bacterial (or infective) endocarditis?
Bacterial endocarditis occurs when bacteria in the bloodstream (bacteremia) lodge on abnormal heart valves or other damaged heart tissue. Certain bacteria normally live on parts of your body, such as the mouth and upper respiratory system, the intestinal and urinary tracts, and the skin. Some surgical and dental procedures cause a brief bacteremia. Bacteremia is
common after many invasive procedures, but only certain bacteria commonly cause endocarditis.
Bacteria are the leading cause of infective endocarditis. Hence, infective endocarditis can more specifically be called bacterial endocarditis. Bacterial endocarditis, in turn, can be classified as either sub acute bacterial endocarditis (SBE) or acute bacterial endocarditis. In cases of sub acute bacterial endocarditis, infection is often with less virulent organisms, such as Streptococcus viridans. More invasive bacteria such as staphylococci result in a more fulminate, faster developing or acute bacterial endocarditis.
Many types of organism can cause infective endocarditis. These are generally isolated by blood culture, where the patient's blood is removed, and any growth is noted and identified. Alpha-haemolytic streptococci, that are present in the mouth will often be the organism isolated if a dental procedure caused the bacteraemia. If the bacteraemia was introduced through the skin, such as contamination in surgery, during catheterisation, or in an IV drug user, Staphylococcus aureus is common.
A third important cause of endocarditis is Enterococcus species. These bacteria enter the bloodstream as a consequence of abnormalities in the gastrointestinal or urinary tracts. Enterococcus species are increasingly recognized as causes of nosocomial or hospital-acquired endocarditis. This contrasts with alpha-haemolytic streptococci and Staphylococcus aureus which are causes of community-acquired endocarditis.
Some organism when isolated give valuable clues to the cause, as they tend to be specific. Candida albicans, a yeast, is associated with IV drug users and the immunocompromised. Pseudomonas species, which are very resilient organisms that thrive in water, are may contaminate street drugs that have been contaminated with drinking water. Streptococcus bovis, which is part of the natural flora of the bowel, tends to present when the patient has bowel cancer. HACEK organisms are a group of bacteria that live on the dental gums, and are associated with IV drug users who contaminate their needles with saliva. |
