# Prosthetic-Valve Endocarditis with Discordant Isolates: A Case Report and a Review of the Literature

## TL;DR

This paper discusses a case of prosthetic-valve endocarditis where blood and valve cultures showed different bacteria, highlighting the importance of blood cultures for diagnosis.

## Contribution

The paper emphasizes the clinical utility of blood cultures over valve cultures in diagnosing prosthetic-valve endocarditis when discordance occurs.

## Key findings

- Blood cultures were more reliable for diagnosis in a case of prosthetic-valve endocarditis with discordant isolates.
- Vancomycin treatment based on blood culture results led to clinical improvement.
- Discordance between blood and valve cultures occurs in 10-29% of cases, often due to contamination or polymicrobial infection.

## Abstract

Prosthetic-valve endocarditis (PVE) represents one of the most serious forms of infective endocarditis, marked by high mortality and considerable management complexity. The 2023 European Society of Cardiology (ESC) Guidelines emphasise the diagnostic centrality of repeatedly positive blood cultures. Nonetheless, a significant area of uncertainty remains regarding the diagnostic and prognostic value of cultures from explanted prosthetic valves—particularly in centres lacking access to molecular diagnostics. Case Presentation: We report a case of prosthetic-valve endocarditis on a bioprosthesis, in which repeated blood-culture sets yielded Streptococcus acidominimus, whereas culture of the explanted valve revealed Staphylococcus warnerii. The patient received six weeks of intravenous vancomycin, with treatment tailored according to the patient’s clinical and laboratory parameters and in alignment with international endocarditis guidelines, obtaining a clear clinical and laboratory improvement. Discussion: The literature reports that discordance between blood-culture and valve-culture results in infective endocarditis may range from approximately 10% to 29%, attributable to contamination, biofilm formation or polymicrobial infection. In our case, management guided by the microorganism repeatedly isolated from blood cultures proved effective and aligned with the 2023 European Society of Cardiology (ESC) guidelines. The case underlines the importance of a multidisciplinary team and an integrated interpretation of microbiological, clinical and surgical data. Conclusions: Infective endocarditis with discordant isolates presents a complex diagnostic challenge. The etiological diagnosis must rely primarily on the results of blood cultures, whereas valve culture plays a complementary role—useful more for prognostic stratification than for initial diagnostic purposes. A multidisciplinary approach and a critical interpretation of microbiological findings are essential to optimise therapeutic management and improve patient outcomes.