A 48-year-old man develops low-grade fever and fatigue two weeks after dental extraction. Blood cultures grow alpha-haemolytic streptococci that are optochin resistant and bile insoluble. Adherence of this organism to damaged cardiac valves is mediated primarily by:
- A M protein binding fibrinogen
- B Dextran-mediated adhesion to fibrin-platelet vegetations ✓
- C IgA protease cleaving mucosal secretory antibody
- D Capsular sialic acid mimicking host neural tissue
Correct answer: B. Dextran-mediated adhesion to fibrin-platelet vegetations
Explanation
Viridans streptococci such as Streptococcus sanguis produce extracellular dextrans (glucans) from dietary sucrose, and these polymers mediate firm adhesion to damaged endocardial surfaces and to teeth, explaining their role in subacute endocarditis after dental procedures. Optochin resistance and bile insolubility exclude pneumococcus. M protein belongs to Streptococcus pyogenes and IgA protease to pneumococcus and Neisseria.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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