A 68-year-old man develops fever, confusion, and nuchal rigidity. CSF shows neutrophilic pleocytosis, protein 180 mg/dL, glucose 25 mg/dL with simultaneous blood glucose 140 mg/dL. Gram stain shows gram-positive bacilli. Which addition to standard ceftriaxone plus vancomycin therapy is required?

• A Metronidazole
• B Doxycycline
• C Rifampicin
• D Ampicillin ✓

Explanation

Gram-positive bacilli in CSF indicate Listeria monocytogenes meningitis, which is not covered by cephalosporins. Ampicillin must be added to vancomycin plus a third-generation cephalosporin in any patient over 50 years or with impaired cell-mediated immunity, precisely because Listeria is a leading cause in these groups. Metronidazole covers anaerobes such as Bacteroides in brain abscess, not Listeria.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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