What is the most likely cause of subacute bacterial endocarditis?

What is the most likely cause of subacute bacterial endocarditis?

• A. Streptococcus viridans
• B. Staphylococcus aureus
• C. Enterococcus faecalis
• D. Pseudomonas aeruginosa

Answer: (A)

Subacute endocarditis develops slowly because it is usually caused by organisms with lower virulence that seed damaged heart valves and grow gradually on the formed vegetations. The classic culprit is Streptococcus viridans, a group of oral streptococci. They enter the bloodstream from dental work or poor dentition and adhere to valve vegetations via adhesive factors like dextran, then proliferate slowly. This results in a protracted course with symptoms such as low-grade fever, fatigue, and malaise rather than an abrupt, severe illness. In contrast, Staphylococcus aureus tends to cause acute endocarditis with rapid valve destruction, often on normal valves or in intravenous drug users. Enterococcus faecalis can also cause endocarditis, especially after genitourinary or gastrointestinal procedures, and Pseudomonas aeruginosa is more associated with nosocomial or prosthetic-valve infections and tends to be more aggressive. But for the subacute presentation, the most likely agent is Streptococcus viridans.

Subacute endocarditis develops slowly because it is usually caused by organisms with lower virulence that seed damaged heart valves and grow gradually on the formed vegetations. The classic culprit is Streptococcus viridans, a group of oral streptococci. They enter the bloodstream from dental work or poor dentition and adhere to valve vegetations via adhesive factors like dextran, then proliferate slowly. This results in a protracted course with symptoms such as low-grade fever, fatigue, and malaise rather than an abrupt, severe illness.

In contrast, Staphylococcus aureus tends to cause acute endocarditis with rapid valve destruction, often on normal valves or in intravenous drug users. Enterococcus faecalis can also cause endocarditis, especially after genitourinary or gastrointestinal procedures, and Pseudomonas aeruginosa is more associated with nosocomial or prosthetic-valve infections and tends to be more aggressive. But for the subacute presentation, the most likely agent is Streptococcus viridans.