What is the appropriate treatment for an elderly male presenting with altered mental status, fever, and a lumbar puncture showing gram-positive (Gram +), catalase-positive bacilli?

Treatment of Bacterial Meningitis with Gram-Positive Bacilli (Listeria monocytogenes)

The correct answer is B: Ceftriaxone + Ampicillin + Vancomycin. This elderly patient with altered mental status, fever, and CSF showing gram-positive, catalase-positive bacilli has Listeria monocytogenes meningitis, which requires ampicillin as the essential component of therapy.

Pathogen Identification and Clinical Context

• Gram-positive, catalase-positive bacilli in CSF is pathognomonic for Listeria monocytogenes 1, 2
• Listeria is more common in elderly patients and immunocompromised individuals 3, 2
• The elderly are more likely to present with altered consciousness and less likely to have classic meningeal signs like neck stiffness or fever 3

Empirical Antibiotic Selection for Elderly Patients

The combination of vancomycin + ceftriaxone (or cefotaxime) + ampicillin is specifically recommended for elderly patients with suspected bacterial meningitis 3, 2:

• Ampicillin is mandatory because cephalosporins (ceftriaxone/cefotaxime) have NO activity against Listeria monocytogenes 1, 2
• Vancomycin is included to cover potentially resistant Streptococcus pneumoniae, which is common in elderly patients 3, 2
• Ceftriaxone covers other common pathogens including Streptococcus pneumoniae and Neisseria meningitidis 3

Why Other Options Are Incorrect

Option A (Ceftriaxone + Vancomycin + Steroid) is inadequate because it lacks ampicillin, leaving Listeria completely untreated 3, 1, 2:

• Cephalosporins do not penetrate Listeria and will result in treatment failure 1
• While steroids (dexamethasone) are recommended for bacterial meningitis, they should be stopped if Listeria is confirmed 2, 4

Option C (Ceftriaxone + Vancomycin) is inadequate for the same reason—no Listeria coverage 3, 2

Option D (Ampicillin alone) is inadequate because it does not cover resistant pneumococcus or other common pathogens in elderly patients 3, 2:

• Monotherapy with ampicillin would miss penicillin-resistant Streptococcus pneumoniae 2

Timing and Administration

• Antibiotics must be administered immediately after blood cultures are obtained, even before lumbar puncture if there is any delay 3, 5
• Bacterial meningitis is a neurologic emergency, and delayed treatment increases mortality and morbidity 3, 6
• If lumbar puncture is delayed for CT imaging or other reasons, empirical therapy should be started first 3, 5

Adjunctive Dexamethasone Considerations

• Dexamethasone should be given before or with the first antibiotic dose for suspected bacterial meningitis 3, 2, 4
• However, dexamethasone must be discontinued if Listeria monocytogenes is confirmed, as it may worsen outcomes in Listeria meningitis 2

Critical Pitfall to Avoid

The most common error is omitting ampicillin from the empirical regimen in elderly patients 3, 2:

• Listeria accounts for a significant proportion of bacterial meningitis in patients over 50 years old 3, 2
• Failure to include ampicillin results in no coverage for this pathogen and predictable treatment failure 1, 2