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A 14-year-old boy is brought to the emergency department by his parents because of high fever, headache, and stiff neck for the past 36 hours. He has become confused over the course of the morning. He uses no medications, has no allergies, and is not sexually active. On examination, he has a temperature of 38 C, moderate nuchal rigidity, and marked photophobia. Lumbar puncture is performed, and the cerebrospinal fluid shows: WBC 3500 with 95% PMNs, elevated protein, decreased glucose, and gram-positive cocci in pairs and short chains. By which of the following mechanisms does this organism mediate its attachment to the respiratory mucosa?



A. Production of a C carbohydrate
B. Production of a hemolytic exotoxin
C. Production of a hyaluronic acid capsule
D. Production of an IgA protease
E. Production of an M protein
Asked by Ewing on Sep 09, 2016

This question is part of

USMLE microbiology prt 8

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1 Answer

John Smith

John Smith

Answered on Sep 09, 2016

production of an iga protease-the correct answer is d. this is a case of streptococcus pneumoniae meningitis. this organismis able to attach to the respiratory mucosa because it has teichoic acids in its envelope, andbecause it produces an iga protease. the iga protease physically cleaves the immunoglobulinmolecules, leaving the fc parts to coat the bacterium. this allows the organisms to bind to thefc receptors on various mucosal cells.streptococcus pneumoniae does not produce a c carbohydrate (choice a), and thus cannot begrouped by the lancefield terminology.although the organism does produce the pneumolysin, which is an alpha-hemolytic exotoxin(choice b), this toxin mediates damage to the respiratory epithelium and inhibition ofleukocytic responses, not attachment to the mucosa.streptococcus pneumoniae does not produce an hyaluronic acid capsule (choice c); streptococcuspyogenes does. most capsules serve to inhibit phagocytosis, rather than to mediate adhesion.only the group a streptococci possess an m protein (choice e), which is used to type them andhelps inhibit phagocytosis.
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