Endogenous oral flora is the likely source of infection for which organism causing endocarditis?

• A. Enterococcus faecalis
• B. Aggregatibacter aphrophilus
• C. Staphylococcus aureus
• D. Pseudomonas aeruginosa

Answer: (B)

Endocarditis from endogenous sources happens when bacteria that normally live in our bodies enter the bloodstream and seed the heart valves. The organism that fits the description of coming from the oral microbiota is Aggregatibacter aphrophilus. It resides in the mouth and is a member of the HACEK group, which are classic causes of subacute endocarditis tied to the oropharyngeal flora. These organisms can enter the bloodstream during dental procedures or from poor dentition and then establish infection on heart valves, sometimes with culture results that are slow to grow and require special techniques. The other organisms listed are not primarily oral residents: Enterococcus faecalis is more commonly linked to GI/urogenital sources; Staphylococcus aureus often originates from skin/mucous membranes and typically causes more acute endocarditis; Pseudomonas aeruginosa is largely environmental and nosocomial rather than a regular component of oral flora.