Which organism is most likely responsible for infective endocarditis in a patient with a cardiac valve prosthesis and positive cultures for catalase-positive, coagulase-negative cocci?

Staphylococcus epidermidis is the organism most commonly associated with infective endocarditis in patients who have cardiac valve prostheses. This species is a type of coagulase-negative staphylococcus, which is typically part of the normal skin flora. In the context of prosthetic devices, such as heart valves, it can act as an opportunistic pathogen.

The positive cultures for catalase-positive and coagulase-negative cocci specifically point toward Staphylococcus species. While Staphylococcus aureus is also a catalase-positive cocci, it is a more virulent organism that is less commonly associated with prosthetic valve endocarditis compared to Staphylococcus epidermidis.

Staphylococcus saprophyticus primarily causes urinary tract infections and is not a typical cause of infective endocarditis, especially in patients with prosthetic materials. Streptococcus pneumoniae, on the other hand, is a significant pathogen in other types of infections, such as pneumonia and meningitis, but it does not have a strong association with infective endocarditis in the context of prosthetic heart valves. Thus, Staphylococcus epidermidis emerges as the most likely organism responsible in this clinical scenario due to its opportunistic nature and common occurrence in