A 25-year-old man presents with fever, headache, neck stiffness, and photophobia for 2 days. CSF analysis shows: glucose 25 mg/dL (simultaneous blood glucose 90 mg/dL), protein 200 mg/dL, and 1500 neutrophils/μL. Gram stain shows gram-positive diplococci. Which organism is the most likely cause?
- A Neisseria meningitidis
- B Streptococcus pneumoniae ✓
- C Haemophilus influenzae
- D Listeria monocytogenes
Correct answer: B. Streptococcus pneumoniae
Explanation
The CSF profile shows low glucose, high protein, and neutrophilic pleocytosis consistent with acute bacterial meningitis. Gram-positive diplococci on Gram stain most likely indicate Streptococcus pneumoniae, the most common cause of bacterial meningitis in adults. N. meningitidis appears as gram-negative diplococci. H. influenzae is gram-negative coccobacillus. Listeria is gram-positive bacillus and typically causes meningitis in neonates, elderly, or immunocompromised patients.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.