Medical MCQ - A 24-year-old woman presents with a 3-day history of fever and cough with rust-colored sputum. He had splenectomy 1 year ago. CXR film indicates consolidation of right lower lobe. Blood cultures are positive for alpha hemolytic gram-positive diplococci. Immunity to the causative organism is based on

A 24-year-old woman presents with a 3-day history of fever and cough with rust-colored sputum. He had splenectomy 1 year ago. CXR film indicates consolidation of right lower lobe. Blood cultures are positive for alpha hemolytic gram-positive diplococci. Immunity to the causative organism is based on

Alternative complement pathway activation

Antibody to fimbriae

IgA antibodies to C carbohydrate

IgG antibodies to a surface acidic polysaccharide

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Correct Answer:

IgG antibodies to a surface acidic polysaccharide

Description:

This is a history of pneumonia due to S. pneumoniae. The most impoant virulence factor of this organism is capsule. Therefore IgG antibodies to the capsular antigen are protective. Other virulence factors produced by pneumococcus include pneumolysin and amidase (also known as suicidal enzyme).

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