What organism is most commonly recovered as a gram-positive cocci from blood cultures of patients with endocarditis?

Enterococcus faecalis is the organism most commonly recovered as a gram-positive cocci from blood cultures of patients with endocarditis. This species is a member of the normal intestinal flora but can be opportunistic pathogens, particularly in individuals with predisposing conditions such as heart valve abnormalities or previous heart disease.

Enterococcus faecalis is known for its ability to form biofilms on heart valves, which facilitates its role in endocarditis, making it a frequent isolate in cases of this infection. Additionally, it exhibits notable antibiotic resistance, which can complicate treatment approaches.

In contrast, while Streptococcus agalactiae can be involved in infections, it is more commonly associated with neonatal infections and does not have the same prevalence in endocarditis cases in adults. Clostridium perfringens is primarily recognized for causing gas gangrene and is anaerobic, and Pediococcus spp. are generally less associated with human disease compared to Enterococcus. Thus, Enterococcus faecalis is the correct answer due to its specific role and prevalence in endocarditis-related bloodstream infections.