Final answer:
Culture-negative endocarditis can be due to prior antibiotic use, infections caused by fastidious organisms, the HACEK group of bacteria, or non-infectious causes that mimic infective endocarditis.
Step-by-step explanation:
The most common causes of culture-negative endocarditis are situations where the causative bacteria are not detectable using standard blood culture techniques. This can occur due to prior antibiotic use, which suppresses the bacterial growth making them difficult to culture, or infections caused by fastidious organisms that require specific culture conditions not employed in the routine practice. Additionally, certain bacteria such as the HACEK group (Haemophilus spp., Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae) and other atypical pathogens may also be responsible for a proportion of culture-negative cases. Non-infectious causes that can mimic infective endocarditis, like marantic endocarditis or thrombotic nonbacterial vegetation associated with systemic autoimmune conditions, can also lead to culture-negative results.