Common organisms in infective endocarditis (IE)

Infective endocarditis on native valves – prevalence of organisms:

This cross-sectional view shows vegetations (accumulations of bacteria and blood clots) on the four valves of the heart. [Source]

• Streptococci 
• Viridans group 10–15%
• Enterococci 20–25%
• Other
• Staphylococci 
• Staphylococcus aureus 9–27%
• Coagulase-negative 1–3%
• Gram-negative bacilli
• Haemophilus spp. 3–8%
• Anaerobes less than
• Rickettsia/fungi 2%

Subacute endocarditis
Members of the viridans group of streptococci are the commonest cause of subacute endocarditis on native valves. These commensals of the upper respiratory tract may enter the bloodstream on

• chewing, 
• tooth brushing or 
• at the time of dental treatment.

Acute endocarditis

Staphylococcus aureus is a common cause of acute endocarditis originating from

• skin infections, 
• abscesses, 
• vascular access sites or 
• intravenous drug misuse.

Postoperative endocarditis
Staphylococcus epidermidis is the most common organism causing postoperative endocarditis following cardiac surgery.