Diversity of Bacterial Agents in Leaflets of Epoxy-Treated Bioprosthetic Heart Valves Removed due to Structural Valvular Degeneration

Abstract Aim. To study the taxonomic composition of bacteria present in the leaflets of bioprosthetic heart valves (BHVs) explanted due to structural valve degeneration (SVD). Materials and methods. Eleven BHVs removed from a matched number of recipients undergoing repeat mitral valve replacement were studied. Gram staining of histological sections was used to visualize bacteria in the BHV leaflets. The nature of inflammatory infiltration in the valves was assessed by immunohistochemistry using the NovoLink Polymer DS reagent kit and antibodies to macrophage and neutrophil markers (CD68 and neutrophil myeloperoxidase, respectively). The taxonomic composition of the microbiota in the explanted BHVs was studied using 16S rRNA metabarcoding. Statistical processing of the results was performed in the GraphPad Prism 8 program; quantitative indicators were recorded as medians, percentiles, minimum and maximum values (Me [Q1–Q3; min–max]). Results. The average lifespan of the studied BHVs was 160 [89–184; 63–221] months. Macroscopic analysis confirmed the presence of changes typical for SVD (ruptures and calcium deposits) in their leaflets with the absence of vegetations typical for prosthetic valve endocarditis (PE). A sharp predominance of macrophages and the presence of single neutrophils within the inflammatory cellular infiltrates also corresponded to the diagnosis of SVD, but not PE. Bacterial colonies located near fibrin deposits were noted in all valves. Metagenomic sequencing revealed DNA of bacteria from 106 genera, with an average of 37 [35–40; 31–44] taxa per BHV. The main contaminants of BHVs, accounting for more than 1% of the total bacterial DNA in more than 50% of the valves, included bacteria from 9 genera: Acinetobacter, Agrobacterium, Aquabacterium, Corynebacterium, Micrococcus, Pseudomonas, Roseateles, Sphingobium, and Sphingomonas. The genera Pseudomonas and Sphingomonas were the most abundant among them with relative DNA shares of 13.7 [12.4–15.1; 10.4–18.2]% and 47.7 [33.7–50.0; 25.8–58.2]%, respectively. Conclusions. A wide range of bacterial agents are present in the leaflets of BHVs with classic signs of SVD. The clinical significance of bacterial invasion remains unclear; however, most of the identified microorganisms are opportunistic pathogens and, under certain conditions, can trigger the development of PE.