Infective endocarditis is most often caused by a:

Infective endocarditis is primarily caused by bacterial infections, making bacteria the most common etiology for this condition. The heart's endocardium, which lines the heart chambers and valves, can become infected when bacteria enter the bloodstream and adhere to a damaged area of the heart. Streptococcus viridans, Staphylococcus aureus, and Enterococcus are among the bacteria frequently implicated in cases of infective endocarditis.

While fungi, viruses, and rickettsiae can cause infections and be involved in other pathological conditions, they are not the predominant causative agents for infective endocarditis. Fungal endocarditis does occur but is significantly less common and usually affects individuals who are immunocompromised or have specific risk factors. Viral infections generally do not lead to endocarditis; instead, they may cause myocarditis or other cardiac issues. Rickettsia species are primarily associated with different disease processes, particularly those transmitted by arthropod vectors, and are not typically linked to endocarditis.

In summary, the predominance of bacterial pathogens in cases of infective endocarditis highlights the importance of recognizing and treating bacterial infections effectively to prevent serious complications associated with this condition.