A 51 year old farmer presents with low-grade fever and a recent history of weight loss. He has been investigated by his GP and general physicians but no cause has been identified for his symptoms. His inflammatory markers are raised and a TTE shows a 0.5 × 0.3 cm echogenic mass attached to the non-coronary cusp of the aortic valve. Endocarditis is suspected, although multiple blood cultures are negative.
Which one of the following organisms is the most likely cause of persistently negative cultures?
A. Streptococcus constellatusInfective endocarditis associated with constantly negative blood cultures can be caused by intracellular bacteria such as Coxiella burnetii, Bartonella, Chlamydia, and, as recently demonstrated, Tropheryma whipplei. These account for up to 5% of all IE. Diagnosis in such cases relies on serological testing, cell culture,or gene amplification. The HACEK group (Haemophilus parainfluenzae, H.aphrophilus, H.paraphrophilus, H.influenzae, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae, and K.denitrificans), Brucella, fungi, and nutritionally variant streptococci may also cause infective endocarditis that is frequently associated with negative blood cultures.