Organisms characteristically causing infective endocarditis

• Viridans group streptococci are the most common cause in non-IVDU without intracardiac prosthetic material.
• Streptococcus bovis group (up to 40% are associated with colorectal tumours, including carcinoma), Staphylococcus aureus (the chance of having infective endocarditis is 30% with community-acquired infection and 10% in hospital-acquired infection) or after implantation of a pacemaker or prosthetic valve.
• Coagulase-negative staphylococci are the commonest cause of contaminated blood cultures, but are common causes of endocarditis in patients with prosthetic valves or pacemakers.
• Enterococcus faecalis – common in older age groups.

The list is potentially almost endless, but common organisms cultured from blood triggering inappropriate requests for echocardiography are:

• Pseudomonas aeruginosa (usually associated with I.V. line infections or pneumonia)
• E. coli and other colifoms (usually associated with urinary, biliary or intra-abdominal infections)
• Streptococcus milleri group (commonly associated with hepatic and other abdominal abscesses)