A silent culprit: Prosthetic valve endocarditis due to Cutibacterium acnes

Cutibacterium acnes is an infrequent cause of infective endocarditis, mainly affecting patients with prosthetic valves. It's unusual and slow-developing clinical presentation often leads to misdiagnosis as culture-negative endocarditis, causing delayed or inadequate treatment and worse outcomes. We report a man in his early fifties with a history of bicuspid aortic valve with prior surgical replacement due to group B streptococcal endocarditis, who presented to outpatient cardiology with one week of worsening shortness of breath. His ischemic evaluation was unremarkable. Transthoracic echocardiography showed a mildly reduced left ventricular ejection fraction and a leak in the bioprosthetic valve. Transesophageal echocardiography showed a suspicious mass suggestive of a vegetation and a perivalvular abscess. Initial infective workup, including blood cultures, was negative. Suspecting prosthetic valve infective endocarditis, he underwent surgical exploration and valve replacement. Cultures of surgical aortic tissue grew C. acnes in 1 of 3 sampled culture bottles. The infection was treated with antibiotics guided by infectious disease specialists. This case underscores the diagnostic and management challenges of C. acnes endocarditis.