Platelets and Platelet Inhibitors in Infective Endocarditis

Haemophilus parainfluenzae Endocarditis Associated With Maxillary Sinusitis and Complicated by Cerebral Emboli in a Young Man

HACEK endocarditis is often difficult to diagnose given the slow-growing characteristics of the organisms involved. Haemophilus parainfluenzae, one of the HACEK organisms, is an uncommon cause of endocarditis. We describe a case of a previously healthy young man with H parainfluenzae endocarditis that was associated with maxillary sinusitis and severe systemic complications, including septic cerebral emboli and mitral valve perforation. Previously reported cases have also described a predilection for younger people, cardiac valve pathology, and a high prevalence of stroke.

Incidence and predictors of Melody® valve endocarditis: a prospective study

BACKGROUND

Percutaneous pulmonary valve replacement (PPVR) has achieved standard of care for the management of dysfunctional right ventricular outflow tract.

AIM

Because of increasing reports of Melody(®) valve (Medtronic, Inc., Minneapolis, MN, USA) infective endocarditis (IE), we aimed to evaluate its incidence and predictors of occurrence.

METHODS

We collected data on all patients who received a Melody valve in the pulmonary position from 2009 to 2012.

RESULTS

A total of 86 consecutive patients underwent PPVR from 2009 to 2012; of these, five developed IE (5.8%). Freedom from IE was 91% at 50 months. Baseline demographics, type of conduit, PPVR procedural success, residual gradients and in situ duration of Melody valve were similar in IE and non-IE patients. A significant number of IE patients had additional unprotected invasive procedures during follow-up and abruptly discontinued antiplatelet therapy (P=0.0139 and P=0.002, respectively). The cumulative probability of survival without cardiovascular events for IE patients was 20% at 20 months, compared with 98.1% for non-IE patients (P<0.0001). Death was statistically associated with IE.

CONCLUSION

Early- and late-onset IE of the Melody valve is emerging as a catastrophic complication of PPVR. Abrupt aspirin discontinuation and additional unprotected invasive procedures during follow-up are significant predictors of Melody valve IE. Owing to its rapidly progressive nature, aggressive invasive management should not be delayed.

Pathology and localization of Avibacterium endocarditidis in experimentally infected broiler breeders

The aim of this study was to investigate the pathogenic potential of Avibacterium endocarditidis. Forty broiler breeders were inoculated with one of three doses of the organism and killed at different time points. Bacteriology, pathology and fluorescence in-situ hybridization (FISH) were performed to evaluate bacterial growth and the development of lesions. Abundant growth in pure culture of A. endocarditidis was always obtained from valvular lesions, while only poor growth or no growth was obtained from liver and spleen lesions, confirming previous observations from naturally occurring cases. Gross lesions and histopathological findings confirmed previous observations. Valvular lesions were acute, ranging from slight thickening of the valves to severe inflammation. In most cases, bacteria colonized the valves. Lesions observed in the spleen included different degrees of necrosis and liver lesions ranged from very small infarcts to large areas of coagulative necrosis. Arthritis occurred in 19 birds, 15 of which tested positive for A. endocarditidis. Most birds developed bacteraemia, but the inability to isolate bacteria from the liver and spleen and the lack of bacteria demonstrated by FISH and histopathology, suggested lack of fulminant septicaemia. A significant correlation between the size of dose inoculated and development of valvular endocarditis was not observed; however, regressive changes in the ovary, liver necrosis and hepato-, spleno- and renomegaly were significantly dose dependent. A. endocarditidis represents a potential pathogen for chickens, the reservoir of which remains to be determined.

Identification of virulence determinants for endocarditis in Streptococcus sanguinis by signature-tagged mutagenesis

Streptococcus sanguinis is a gram-positive, facultative anaerobe and a normal inhabitant of the human oral cavity. It is also one of the most common agents of infective endocarditis, a serious endovascular infection. To identify virulence factors for infective endocarditis, signature-tagged mutagenesis (STM) was applied to the SK36 strain of S. sanguinis, whose genome is being sequenced. STM allows the large-scale creation, in vivo screening, and recovery of a series of mutants with altered virulence. Screening of 800 mutants by STM identified 38 putative avirulent and 5 putative hypervirulent mutants. Subsequent molecular analysis of a subset of these mutants identified genes encoding undecaprenol kinase, homoserine kinase, anaerobic ribonucleotide reductase, adenylosuccinate lyase, and a hypothetical protein. Virulence reductions ranging from 2-to 150-fold were confirmed by competitive index assays. One putatively hypervirulent strain with a transposon insertion in an intergenic region was identified, though increased virulence was not confirmed in competitive index assays. All mutants grew comparably to SK36 in aerobic broth culture except for the homoserine kinase mutant. Growth of this mutant was restored by the addition of threonine to the medium. Mutants containing an insertion or in-frame deletion in the anaerobic ribonucleotide reductase gene failed to grow under strictly anaerobic conditions. The results suggest that housekeeping functions such as cell wall synthesis, amino acid and nucleic acid synthesis, and the ability to survive under anaerobic conditions are important virulence factors in S. sanguinis endocarditis.

Fluid Shear Regulates the Kinetics and Receptor Specificity ofStaphylococcus aureusBinding to Activated Platelets

The interaction between surface components on the invading pathogen and host cells such as platelets plays a key role in the regulation of endovascular infections. However, the mechanisms mediating Staphylococcus aureus binding to platelets under shear remain largely unknown. This study was designed to investigate the kinetics and molecular requirements of platelet-S. aureus interactions in bulk suspensions subjected to a uniform shear field. Hydrodynamic shear-induced collisions augment platelet-S. aureus binding, which is further potentiated by platelet activation with stromal derived factor-1beta. Peak adhesion efficiency occurs at low shear (100 s(-1)) and decreases with increasing shear. The molecular interaction of platelet alpha(IIb)beta(3) with bacterial clumping factor A through fibrinogen bridging is necessary for stable bacterial binding to activated platelets under shear. Although this pathway is sufficient at low shear (</=400 s(-1)), the involvement of platelet gpIb and staphylococcal protein A through von Willebrand factor bridging is essential for optimal recruitment of S. aureus cells by platelets in the high shear regime. IgG plays an inhibitory role in the adhesion process, presumably by interfering with the binding of von Willebrand factor to staphylococcal protein A. This study demonstrates that platelet activation and a fluid-mechanical environment representative of the vasculature affect platelet-S. aureus cell-adhesive interactions pertinent to the process of S. aureus-induced bloodstream infections.