Endocarditis Due to Abiotrophia Defectiva: Rare Case Report With Fatal Outcome

Infective endocarditis is a condition with high morbidity and mortality, predominantly caused by gram-positive microorganisms such as Streptococcus, Staphylococcus aureus, and coagulase-negative staphylococci. Abiotrophia defectiva (a gram-positive organism) is a rare pathogen, accounting for only 1–2% of endocarditis cases, with few reports in the worldwide literature. This microorganism is associated with a more aggressive clinical course, higher rates of embolic complications, therapeutic failure, and mortality compared with conventional pathogens. We report the first case of prosthetic-valve endocarditis due to A. defectiva isolated in our institution, which evolved to a fatal outcome. The patient, S.A.S., a 67-year-old man with a bioprosthetic aortic valve implanted 15 years earlier, dyslipidemia, and benign prostatic hyperplasia, presented with an insidious course of weight loss, asthenia, melena, and hematuria. On admission, he had severe renal dysfunction (urea 170 mg/dL, creatinine 6.53 mg/dL), coagulopathy due to warfarin toxicity (INR 6.28), severe anemia (Hb 6.5 g/dL, Hct 18%), leukopenia (4,440/mm³) and elevated inflammatory markers (CRP 52 mg/dL). Echocardiography showed double prosthetic dysfunction with vegetation. Microbiological identification of A. defectiva was performed by MALDI-TOF mass spectrometry, which was fundamental for diagnosing this fastidious organism. Antimicrobial therapy was started with penicillin plus gentamicin without clinical response, and later switched to vancomycin. Coagulopathy correction and hemodialysis were instituted in parallel. The patient underwent urgent valve replacement but evolved with mixed shock (cardiogenic and septic) in the postoperative period, without response to antibiotic and intensive therapy, culminating in death. This case adds to the scarce literature on A. defectiva, highlighting its rarity, diagnostic difficulty, lack of standardized susceptibility testing, and often poor prognosis, and emphasizes the importance of MALDI-TOF in accurate identification of this emerging pathogen.