Complicated Infective Endocarditis of a Mechanical Aortic Valve due to Propionibacterium acnes.

Propionibacterium acnes is known to be a causative microorganism in low-grade and late prosthetic valve endocarditis. Here, the case is reported of a late, apparently culture-negative endocarditis of an aortic mechanical prosthesis, diagnosed to be caused by P. acnes after pan-bacterial polymerase chain reaction (PCR) on the explanted mechanical prosthetic valve. This endocarditis was complicated by an aortic root abscess; after surgical resection a ventricular septal defect (VSD) with overt right ventricular and multiple organ failure occurred. Low suspicion, the failure of routine blood culture to grow P. acnes and erroneous interpretation of P. acnes as contamination, frequently delay the correct diagnosis and treatment of this condition. Hence, although infection with P. acnes is usually indolent, abscess formation and a need for surgery are common.