A 50-year-old diabetic develops meningitis. CSF shows: opening pressure 280 mmH₂O, turbid fluid, protein 220 mg/dL, glucose 18 mg/dL (blood glucose 90 mg/dL), 1800 cells/mm³ predominantly neutrophils. Gram stain shows short gram-positive rods. What is the most likely organism and the treatment?
- A Streptococcus pneumoniae; IV ceftriaxone + vancomycin
- B Haemophilus influenzae; IV ceftriaxone
- C Listeria monocytogenes; IV ampicillin + gentamicin ✓
- D Staphylococcus aureus; IV oxacillin
Correct answer: C. Listeria monocytogenes; IV ampicillin + gentamicin
Explanation
Listeria monocytogenes is a gram-positive rod (not coccus) that causes meningitis in immunocompromised patients (diabetes, extremes of age, pregnancy, steroids); it is intrinsically resistant to cephalosporins, making ampicillin + gentamicin (synergistic bactericidal) the treatment of choice. Standard empirical meningitis regimens (ceftriaxone + vancomycin) may miss Listeria; ampicillin must be added in at-risk populations. H. influenzae would show gram-negative coccobacilli. S. aureus meningitis is gram-positive cocci in clusters.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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