Treatment of Gram-Positive Rod Bacteremia
For gram-positive rod bacteremia, remove any central venous catheter if present and initiate empiric therapy with ampicillin or penicillin, avoiding vancomycin as many gram-positive rods (including Listeria species) are intrinsically vancomycin-resistant. 1
Initial Empiric Antibiotic Selection
The choice of empiric therapy for gram-positive rod bacteremia differs fundamentally from typical gram-positive cocci infections:
Ampicillin or penicillin should be the first-line empiric agents for suspected gram-positive rod bacteremia, as these organisms often include Listeria species, Corynebacterium species, and Bacillus species that may be vancomycin-resistant 1
Vancomycin is NOT appropriate empiric therapy for gram-positive rods, as demonstrated by a case of Listeria grayi bacteremia in a stem cell transplant recipient where vancomycin therapy failed and the organism was resistant to vancomycin but susceptible to ampicillin 1
For immunocompromised patients with suspected gram-positive rod bacteremia, broad-spectrum coverage should include agents active against resistant gram-positive bacteria such as linezolid or daptomycin if MRSA is also a concern, but ampicillin must be included for Listeria coverage 2
Specific Organisms and Targeted Therapy
Listeria Species
- Ampicillin is the drug of choice for Listeria bacteremia, as these organisms are intrinsically resistant to vancomycin 1
- Accurate identification is critical, as Listeria may initially be misidentified as Corynebacterium species 1
Erysipelothrix rhusiopathiae (Erysipeloid)
- Penicillin (500 mg four times daily) or amoxicillin (500 mg three times daily) for 7-10 days is recommended 2
- This organism is resistant to vancomycin, teicoplanin, and daptomycin 2
Corynebacterium Species
- Most Corynebacterium species are susceptible to vancomycin, but susceptibility testing is essential 1
- If persistent bacteremia occurs despite vancomycin, consider alternative identification (such as Listeria) and switch to ampicillin 1
Catheter Management
- All central venous catheters should be removed in cases of gram-positive rod bacteremia, as catheter retention significantly worsens outcomes 2
- For short-term catheters infected with any bacterial pathogen, removal is mandatory 2
Treatment Duration
Standard duration is 7-14 days for uncomplicated gram-positive rod bacteremia after catheter removal 2, 3
Extended therapy (4-6 weeks) is required for patients with:
De-escalation Strategy
- Once culture and susceptibility results are available, narrow therapy to the most appropriate single agent based on susceptibility testing 4, 3
- Continue targeted therapy for the full treatment course rather than maintaining broad empiric coverage 3
Special Populations
Neutropenic/Immunocompromised Patients
- These patients require very broad-spectrum empirical coverage that includes activity against resistant gram-positive bacteria (vancomycin, linezolid, or daptomycin) AND gram-negative bacteria, but ampicillin must be added if gram-positive rods are identified 2
- Coverage for Pseudomonas species with an antipseudomonal beta-lactam is also necessary 2
Critical Pitfalls to Avoid
Do not use vancomycin monotherapy for gram-positive rod bacteremia without culture confirmation, as many species (Listeria, Erysipelothrix) are intrinsically resistant 2, 1
Do not dismiss gram-positive rods as contaminants if they grow in multiple blood cultures—this represents true bacteremia requiring treatment 1
Do not delay switching from vancomycin to ampicillin once Listeria or other vancomycin-resistant gram-positive rods are identified, as persistent inappropriate therapy increases mortality risk 1
Do not retain central venous catheters in patients with gram-positive rod bacteremia, as this significantly worsens outcomes 2