A 22-year-old woman comes to the emergency department due to intermittent fevers and chills over the past few days. Last week, she underwent routine dental cleaning with no complications. The patient has a history of mitral valve prolapse. Temperature is 38.2 C (100.8 F). Physical examination reveals a non-ejection mid-systolic click followed by a late-systolic murmur best heard at the cardiac apex. Blood cultures are drawn and grow gram-positive bacteria that synthesize dextrans from sucrose. Which of the following would be the most likely adherence site for these bacteria?

Question

A 22-year-old woman comes to the emergency department due to intermittent fevers and chills over the past few days.  Last week, she underwent routine dental cleaning with no complications.  The patient has a history of mitral valve prolapse.  Temperature is 38.2 C (100.8 F).  Physical examination reveals a non-ejection mid-systolic click followed by a late-systolic murmur best heard at the cardiac apex.  Blood cultures are drawn and grow gram-positive bacteria that synthesize dextrans from sucrose.  Which of the following would be the most likely adherence site for these bacteria?

Quizplus · Accepted Answer

This patient with mitral valve prolapse (as suggested by the auscultated systolic click and murmur) now has bacteremia following dental cleaning. Viridans streptococci are normal inhabitants of the oral cavity and cause transient bacteremia after dental procedures. These gram-positive organisms are capable of producing extracellular polysaccharides (dextrans) using sucrose as a substrate. Dextrans facilitate streptococcal adherence to fibrin. Fibrin and platelets are deposited at sites of endothelial trauma, providing a site for bacterial adherence and colonization during bacteremia. In patients with pre-existing valvular lesions, viridans streptococci can adhere to the affected valve and establish infection leading to endocarditis. Other factors that facilitate pathogenesis may also be involved. Staphylococcus aureus is more aggressive and can adhere to intact valves. The risk of endocarditis following dental procedures is low with mitral valve prolapse, and antibiotic prophylaxis is not recommended; however, cases can still occur. (Choice A) Circulating heparins prolong the partial thromboplastin time by activating antithrombin III, thereby decreasing thrombin activity and ultimately preventing fibrinogen conversion to fibrin, thereby preventing clot formation. Circulating heparins would not provide a binding site for bacteria. (Choice B) Endothelial surface glycoproteins mediate binding of immune cells to endothelium, facilitated by the expression of cell adhesion molecules on the surface of inflamed endothelium. Neutrophils are then able to bind and migrate between the endothelial cells, followed by monocytes and lymphocytes. (Choices D and E) Subendothelial collagen and glycosaminoglycans form the subendothelial fibrous cap over the central core of an atherosclerotic plaque and are potent platelet activators. When exposed (eg, denuded endothelium in atherosclerotic plaque), they contribute to rapid thrombus formation that can lead to myocardial infarction in a coronary artery. Educational objective: Viridans streptococci are normal inhabitants of the oral cavity and are a cause of transient bacteremia after dental procedures in healthy and diseased individuals. In patients with pre-existing valvular lesions, viridans streptococci can adhere to fibrin-platelet aggregates and establish infection that leads to endocarditis.

A 22-Year-Old Woman Comes to the Emergency Department Due to Intermittent