Dual-Valve Infective Endocarditis Caused by Carbapenem-Resistant Acinetobacter baumannii in a Patient with Bicuspid Aortic Valve: A Case Report

Abstract Background Infective endocarditis (IE) caused by carbapenem-resistant Acinetobacter baumannii (CRAB) is rare and associated with substantial mortality. When it arises on a bicuspid aortic valve (BAV), simultaneously involves the aortic and mitral valves, and presents with persistently negative blood cultures, diagnosis and management become exceptionally challenging. Case presentation A 52-year-old man presented with a four-month history of fever and positive rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies, initially raising suspicion of rheumatoid arthritis. Transesophageal echocardiography revealed a BAV (right–left cusp fusion), a large mitral anterior leaflet vegetation (1.5 × 1.3 cm), and aortic valve vegetations. Splenic and cerebral infarctions were subsequently identified. Blood cultures remained repeatedly negative in the context of antecedent antimicrobial exposure. He underwent double mechanical valve replacement with vegetation debridement, and intraoperative valve tissue culture grew CRAB, prompting adjustment to a high-dose sulbactam-based regimen. He recovered and was discharged. To our knowledge, this combination of culture-negative CRAB native-valve IE, BAV, dual-valve involvement, and diagnosis solely by intraoperative tissue culture has not previously been reported. This case illustrates a plausible anatomical mechanism linking BAV to concomitant aortic–mitral involvement, highlights the diagnostic value of intraoperative tissue culture and the importance of timely surgical evaluation, and underscores the potential for positive rheumatoid serology to complicate the diagnostic process.