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Background
Invasive mold infections are a well-known and life-threatening condition after allogeneic hematopoietic stem cell transplantation (HSCT). While Aspergillus species are recognized as predominant pathogens, Fusarium species should also be considered due to their broad environmental distribution and the expected poor outcome of invasive fusariosis. Particularly, splenic rupture as a complication of disseminated disease has not been reported yet.
Case presentation
Two weeks after allogeneic HSCT for severe aplastic anemia, a 16-year-old boy presented with painful, erythematous skin nodules affecting the entire integument. As disseminated mycosis was considered, treatment with liposomal amphotericin B and voriconazole (VCZ) was initiated. Invasive fusariosis was diagnosed after histological and previously unpublished polymerase chain reaction-based examination of skin biopsies. Microbiological tests revealed Fusarium solani species. Despite stable neutrophil engraftment and uninterrupted treatment with VCZ, he developed mold disease-associated splenic rupture with hypovolemic shock and fungal endocarditis. The latter induced a cardiac thrombus and subsequent embolic cerebral infarctions with unilateral hemiparesis. Following cardiac surgery, the patient did not regain consciousness because of diffuse cerebral ischemia, and he died on day +92 after HSCT.
Conclusion
Invasive fusariosis in immunocompromised patients is a life-threatening condition. Despite antimycotic treatment adapted to antifungal susceptibility testing, the patient reported here developed uncommon manifestations such as splenic rupture and fungal endocarditis.
Staphylococcus aureus (S. aureus) endocarditis is still one of the most fatal heart diseases, with a mortality rate of 20-45%. In recent years, the importance of endothelial cells (ECs) in the context of endocarditis has become more evident. The vascular endothelium forms a selective barrier between blood and the adjacent tissue by maintaining an anti-inflammatory and anti-thrombogenic phenotype. However, in case of insertion of cardiac implants, an injury of the endothelium can occur which promotes platelet aggregation followed by S. aureus adherence to the platelets, especially in areas with low hemodynamic shear stress. This process is considered as a key event in the development of infective endocarditis (IE) and allows bacteria to colonize the heart valves. Despite extensive research, the pathogenesis of IE is still not completely understood. Therefore, further investigations are needed to enable an effective prevention of this life-threatening disease.
In order to study the infection process of S. aureus, internalization experiments with two different S. aureus strains, one control strain (HG001) and one strain isolated from an endocarditis patient (T-72949) were performed in human coronary artery endothelial cells (HCAEC). Subsequently, an extensive proteome analysis of the host cells was carried out. More specific analyses were performed using peptidoglycan (PGN), a cell wall component of Gram-positive bacteria, which causes a pro-inflammatory response in ECs. In this context, the focus remained on the analysis of cellular changes in terms of cell stiffness, wound healing, and additionally platelet aggregation.
The analysis of the HCAEC host proteome revealed a time-related difference depending on the infecting bacterial strain. Several proteins involved in host cell signaling pathways exhibited a higher abundance at earlier time points in host cells infected with endocarditis strain T-72949 compared to those infected with HG001. Further proteome analysis uncovered several adaptations on the cellular side that enable internalization and replication of both S. aureus strains as well as the activation of pathways that promote cellular recovery. Furthermore, it could be shown that PGN reduced cellular stiffness which could lead to an increased bacterial uptake and would thereby promote the development of a chronic S. aureus infection. Additionally, PGN prevented effective wound healing which promotes a pro-thrombotic and pro-inflammatory condition. This status could facilitate the bacterial infection of further cells. Apart from that, PGN induced platelet aggregation which could ease bacterial adhesion to thrombotic surfaces (e.g., dysfunctional endothelium). The following formation of a mature vegetation might protect the bacteria from the immune system and antibiotics.
The results of the present work emphasize the central role of ECs in the context of IE. It could be demonstrated that a healthy monolayer of ECs enables a beneficial cell response and may prevent the development of vascular diseases. Moreover, the comprehensive proteome dataset which was generated in this project provides a valuable source of information for future studies to unravel further molecular mechanisms of endocarditis and possible therapeutic approaches.