A 25-year-old immunocompetent patient develops acute bacterial meningitis with Gram-positive diplococci on CSF Gram stain. The most common mechanism by which Streptococcus pneumoniae crosses the blood-brain barrier is:
- A Transcytosis via platelet-activating factor receptor on choroid plexus endothelium ✓
- B Paracellular route after complement-mediated tight junction disruption
- C Trojan horse mechanism within infected monocytes crossing the BBB
- D Direct invasion through peripheral nerve sheaths (perineural route)
Explanation
S. pneumoniae traverses the blood-brain barrier primarily by binding platelet-activating factor receptor (PAFr) on brain capillary endothelial cells via phosphorylcholine in the pneumococcal cell wall teichoic acid; this promotes receptor-mediated transcytosis (transcytosis in membrane-bound vesicles) into the CNS. Bacteria may also use the choroid plexus. Paracellular invasion requires tight junction disruption but is not the primary mechanism for pneumococcus. The Trojan horse mechanism (cell-to-cell) is used by HIV, Listeria, and CMV. Perineural spread is used by herpes simplex virus.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.