The blood cultures obtained from this patient on admission grow Streptococcus species. Which of the following processes was the most likely initiating step in the pathogenesis of this patient's condition?

Question

The blood cultures obtained from this patient on admission grow Streptococcus species.  Which of the following processes was the most likely initiating step in the pathogenesis of this patient's condition?

Quizplus · Accepted Answer

The initial process involved in the pathogenesis of infective endocarditis (IE) is a disruption of normal endocardial surface. This occurs most commonly at the areas of maximal turbulence to blood flow in preexisting valvular lesions, typically the atrial surface of incompetent atrioventricular valves or the ventricular surface of incompetent semilunar valves. This is followed by focal adherence of fibrin and platelets, forming a sterile fibrin-platelet nidus. During bacteremia from any cause, microorganisms colonize the sterile nidus on the endothelial surface with subsequent microbial growth leading to further activation of the coagulation system. Streptococci infect the cardiac valves with preexisting endothelial lesions. In contrast, Staphylococcus aureus can adhere to damaged or normal endothelial cells. Macroscopic vegetations consist of fibrin and platelets on the surface, with red blood cell debris, leukocytes, and clusters of microorganisms embedded deep within the lesion. (Choice A) Endomyocardial fibrosis is a restrictive cardiomyopathy characterized by thickening and fibrosis of the apical endocardial surface. It occurs most commonly in tropical regions (eg, Uganda). (Choices C and E) Neutrophil-rich inflammatory infiltrates with subsequent abscess formation and/or liquefactive necrosis of underlying cardiac tissue are common in advanced lesions. (Choice D) Myxomatous degeneration of the mitral valve is characterized by thickened and redundant mitral leaflets with elongated chordae leading to prolapse of one or both mitral leaflets (mitral valve prolapse). Myxomatous degeneration can predispose patients to the development of endocarditis; however, endocarditis vegetations themselves are not formed through myxomatous degeneration. Educational objective: Vegetations are caused by bacterial colonization and growth on a sterile fibrin-platelet nidus that forms on the damaged/disrupted endothelial surface of the valvular apparatus. __________ References: Pathogenesis of streptococcal and staphylococcal endocarditis. (http://www.ncbi.nlm.nih.gov/pubmed/12092474) Mechanisms of infective endocarditis: pathogen-host interaction and risk states. (http://www.ncbi.nlm.nih.gov/pubmed/24247105)

The Blood Cultures Obtained from This Patient on Admission Grow