Microbiology MCAT Practice Question
A 24-year-old man presents to the emergency department with fever, severe headache, and nuchal rigidity. Physical examination reveals a petechial rash on his trunk and lower extremities. Cerebrospinal fluid shows elevated protein, low glucose, and pleocytosis with predominance of neutrophils. Gram stain of CSF reveals gram-negative diplococci with kidney bean morphology. Culture on Thayer-Martin medium yields oxidase-positive, maltose-fermenting colonies. The organism is confirmed to produce IgA-1 protease and express Opa proteins. Which of the following best explains why this organism is particularly successful at causing invasive meningococcal disease?
Answer choices
- AIgA-1 protease cleaves the predominant antibody at mucosal surfaces, while Opa proteins mediate adhesion to host cells, allowing initial colonization and subsequent invasion across the blood-brain barrierCorrect answer
- BOpa proteins directly activate the alternative complement pathway, leading to increased vascular permeability and CNS invasion
- CIgA-1 protease enzymatically degrades the blood-brain barrier endothelium, creating direct access to the meninges
- DOxidase production generates reactive oxygen species that inhibit neutrophil chemotaxis, preventing immune recruitment to infected tissues
- EKidney bean morphology provides resistance to osmotic lysis during passage through the blood-brain barrier
- FCEA-related cell adhesion molecule binding triggers apoptosis of meningeal macrophages, eliminating the primary defense mechanism
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