IS-Pro-based pathogen detection in explanted heart valves of suspected endocarditis patients

Accurate pathogen identification in infective endocarditis (IE) is limited, particularly in culture-negative cases. This study evaluated the performance of the Molecular Culture ID (MC-ID) assay in heart valve specimens from patients with suspected IE. Fifty-seven valve specimens from patients with suspected IE were analyzed using conventional culture, 16S/18S rDNA sequencing (SepsiTest, Molzym, Germany), the Biofire Joint Infection Panel (BJP; bioMérieux, Marcy l'Étoile, France), and MC-ID, with previously reported results as comparators. Twelve specimens (21.1%) were culture-positive, and 45 (78.9%) were culture-negative. MC-ID showed 83.3% positive agreement and 44.4% negative agreement with culture, achieving species-level concordance in 8/12 cases. Three culture-positive/MC-ID-negative results reflected organisms outside the assay's detection range or limited taxonomic resolution. MC-ID detected pathogens in 25/45 (55.5%) culture-negative specimens; 21 were corroborated by PCR and/or BJP. Discrepancies largely reflected polymicrobial infections or taxonomic resolution limits. MC-ID identified pathogens in four PCR-/BJP-negative specimens, of which three likely were of clinical significance. MC-ID was negative in two culture-negative, PCR-/BJP-positive specimens. MC-ID can improve pathogen detection in both culture-positive and culture-negative IE, complementing conventional and molecular diagnostics and providing a comprehensive microbiological assessment in suspected IE cases.IMPORTANCEInfective endocarditis (IE) remains difficult to diagnose, especially when blood and tissue cultures fail to identify a pathogen. Accurate organism detection is essential for guiding targeted therapy and reducing reliance on broad-spectrum antibiotics. This study shows that the Molecular Culture ID (MC-ID) assay markedly improves diagnostic yield in culture-negative valve specimens, frequently identifying pathogens missed by conventional and molecular tests. MC-ID also clarifies cases complicated by polymicrobial infection or limited taxonomic resolution, providing species-level or clinically actionable identification in many instances. By complementing existing diagnostic methods and expanding detection beyond their constraints, MC-ID offers a more comprehensive microbiological assessment of suspected endocarditis. Its integration into diagnostic workflows has the potential to enhance clinical decision-making and improve management of this high-risk condition.