When standard blood cultures are negative: Sarocladium kiliense endocarditis and the need to consider rare fungal pathogens

Background Blood culture-negative endocarditis remains a major clinical challenge with potentially fatal consequences due to diagnostic difficulty and inadequacy of empirical antibiotic treatment. Case Summary In late 2024, a 75-year-old man underwent aortic and mitral valve replacement with bioprostheses due to methicillin-resistant Staphylococcus epidermidis endocarditis. Six months after cardiac surgery, the patient was admitted to the hospital for suspected ischemic stroke, confirmed on brain computed tomography (CT), with fever and a slight increase in inflammatory biomarkers. Transesophageal echocardiography revealed degeneration of the prosthetic aortic valve, with leaflet thickening and a hyperechoic nodular lesion. CT imaging showed bilateral renal emboli and pleural effusion. Repeated blood cultures, serologic testing for Brucella, Bartonella , Legionella , Mycoplasma pneumoniae , and Coxiella burnetii , as well as screening for autoimmune disease, were negative. Two weeks later, the patient developed acute right iliac artery occlusion requiring urgent revascularization. Finally, repeated extended-incubation blood cultures and culture of the thrombus yielded Sarocladium kiliense , a rare opportunistic filamentous mold, supported by persistently positive serum β-D-glucan. Empirical therapy with liposomal amphotericin B was initiated. Following multidisciplinary discussion, the patient was deemed ineligible for surgery due to clinical deterioration and high operative risk. He was transitioned to palliative care and died shortly thereafter. Conclusion To date, this represents the third case of endocarditis due to S. kiliense reported in the literature. When typical causes of endocarditis and differential diagnoses are excluded, fungal endocarditis should be ruled out with proper microbiological testing, even in immunocompetent patients.