In a patient with symptoms suggestive of bacterial endocarditis, which organism is most likely responsible if alpha hemolysis is noted?

• A. Enterococcus faecalis
• B. Streptococcus pneumoniae
• C. Streptococcus mitis
• D. Staphylococcus aureus

Answer: (C)

In the context of bacterial endocarditis and alpha-hemolytic streptococci, Streptococcus mitis is a significant pathogen. This organism is part of the viridans group streptococci, which are common flora in the oral cavity and can enter the bloodstream through dental procedures, oral trauma, or other means, leading to infective endocarditis.

Alpha hemolysis refers to the partial lysis of red blood cells when cultured on blood agar, producing a greenish discoloration around the colonies. Streptococcus mitis, along with other viridans streptococci, is known for this characteristic hemolytic pattern. Their ability to adhere to damaged heart valves makes them prominent culprits in cases of subacute infective endocarditis, especially in patients with predisposing factors such as existing heart conditions or immunocompromised states.

In contrast, other organisms listed may not typically be associated with alpha hemolysis or bacterial endocarditis. For example, Staphylococcus aureus, while a significant cause of infective endocarditis, is usually associated with beta hemolysis and more aggressive forms of the disease. Enterococcus faecalis (which can be a cause but is not alpha