What is the recommended work-up and antibiotic regimen for listeria (Listeria monocytogenes) bacteremia?

Management of Listeria Monocytogenes Bacteremia

For Listeria monocytogenes bacteremia, treatment should consist of ampicillin or amoxicillin 2g IV every 4 hours for 21 days, with the addition of gentamicin no longer routinely recommended based on recent evidence. 1, 2

Diagnostic Work-up

Blood Cultures

• Obtain multiple sets of blood cultures before starting antibiotics when possible
• Blood culture sensitivity for Listeria is moderate (10-75%) 1
• Repeat blood cultures to document clearance of bacteremia

Cerebrospinal Fluid (CSF) Analysis

• Perform lumbar puncture in all patients with Listeria bacteremia to rule out meningitis
• CSF studies should include:
  • Cell count and differential
  • Protein and glucose
  • Gram stain (sensitivity only 25-35% for Listeria) 1
  • Culture (essential for diagnosis)
  • Consider PCR testing if available

Additional Testing

• CT or MRI of the brain if neurological symptoms are present
• Echocardiography to rule out endocarditis in cases of persistent bacteremia
• Evaluate for potential source (food history, immunosuppression evaluation)

Antibiotic Treatment Algorithm

First-line Treatment

• Ampicillin or amoxicillin 2g IV every 4 hours 1, 2
• Treatment duration: 21 days for bacteremia 1, 2

For Penicillin-Allergic Patients

• Trimethoprim-sulfamethoxazole (10-20 mg/kg of trimethoprim component) in divided doses 1, 3

Important Considerations

• Avoid cephalosporins as they have no activity against Listeria 1, 3
• Dexamethasone should be discontinued if initially started for suspected bacterial meningitis once Listeria is identified 1, 2
• Vancomycin has poor CSF penetration and should not be used for Listeria meningitis 4, 5

Special Patient Populations

Immunocompromised Patients

• Higher doses of ampicillin may be required
• Longer treatment courses (>21 days) may be necessary
• Closer monitoring for treatment failure 2

Pregnant Women

• Ampicillin or amoxicillin is preferred
• Avoid fluoroquinolones 2
• Consider fetal monitoring during treatment

Elderly Patients (>50 years)

• Higher risk population for Listeria infection
• May require dose adjustments based on renal function
• Monitor for adverse effects of antibiotics more closely

Monitoring Response to Treatment

• Daily clinical assessment for fever, neurological symptoms
• Repeat blood cultures to document clearance
• If meningitis is present, consider repeat lumbar puncture to document CSF sterilization in cases of poor clinical response

Common Pitfalls to Avoid

1. Using cephalosporins - Listeria is intrinsically resistant to all cephalosporins 1, 3
2. Continuing dexamethasone - Associated with increased mortality in neurolisteriosis 1, 2
3. Inadequate treatment duration - Shorter courses lead to higher relapse rates
4. Missing CNS involvement - Always evaluate for meningitis in Listeria bacteremia
5. Relying on erythromycin - In vitro studies show antagonism when combined with penicillins 6

By following this evidence-based approach to diagnosis and treatment, mortality and morbidity from Listeria bacteremia can be significantly reduced.