Treatment of Achromobacter xylosoxidans Infections
For Achromobacter xylosoxidans infections, trimethoprim-sulfamethoxazole (TMP-SMZ) or an antipseudomonal beta-lactam (piperacillin-tazobactam, ceftazidime, cefoperazone) should be used as first-line therapy, with carbapenems (meropenem, imipenem) reserved for severe infections or resistant isolates. 1, 2
Antimicrobial Susceptibility Profile
A. xylosoxidans demonstrates a characteristic resistance pattern that guides empiric therapy:
- Susceptible agents: TMP-SMZ, antipseudomonal penicillins (piperacillin-tazobactam), ceftazidime, cefoperazone, and carbapenems (imipenem, meropenem) 1
- Moderately susceptible: Ciprofloxacin 1
- Intrinsically resistant: Aminoglycosides (tobramycin, amikacin, gentamicin), ceftriaxone, cefotaxime, cefoxitin, ceftizoxime, aztreonam 1, 3
The intrinsic aminoglycoside resistance is mediated by the AxyXY-OprZ efflux pump system, which also confers resistance to cefepime, some fluoroquinolones, tetracyclines, and erythromycin 3. This is critical to recognize as aminoglycosides should never be used as monotherapy for A. xylosoxidans.
Recommended Treatment Regimens
Monotherapy Options
Single-agent therapy is effective for most A. xylosoxidans infections 1:
- TMP-SMZ: Appropriate for mild to moderate infections 1, 4
- Piperacillin-tazobactam: Effective for serious infections 4
- Meropenem: Best in vitro activity (92.3% susceptibility), preferred for severe infections or bacteremia 2
- Ceftazidime: Alternative beta-lactam option 1
Combination Therapy
Reserved for severe or complicated infections 4:
- Piperacillin plus TMP-SMZ for pneumonia with empyema (requires prolonged therapy of approximately 1 month) 4
- Consider combination therapy for critically ill patients or those with septic shock 1
Clinical Context and Risk Factors
A. xylosoxidans bacteremia occurs predominantly in specific patient populations 2, 1:
- Immunocompromised hosts: Solid organ cancer (30.7%), chemotherapy recipients 2
- Hospital-acquired infections: Nearly all cases (>90%) 2
- Catheter-related: Central venous catheters present in 46% of cases 2, 1
- Prior antibiotic exposure: 54% of patients 2
The organism is recognized as a pathogen in febrile neutropenic cancer patients 5 and cystic fibrosis patients 5, 3.
Source Control
Catheter removal should be strongly considered for catheter-related A. xylosoxidans bacteremia, particularly if clinical response is inadequate after 2-3 days of appropriate antibiotics 2, 1. Four of 13 patients (30.7%) in one series had intravascular catheter-related infections 2.
For persistent or recurrent bacteremia, investigate for deep-seated foci such as infected lymph nodes, which can serve as a reservoir for relapsing infection 6.
Duration of Therapy
- Standard bacteremia: 2-3 weeks of intravenous therapy 2
- Complicated infections (pneumonia with empyema): Prolonged therapy up to 1 month may be required 4
- Catheter-related infections: Continue antibiotics for at least 10-14 days after catheter removal 2
Prognostic Factors
All-cause 30-day mortality is 23.1% overall but varies by clinical presentation 2:
- Primary bacteremia: 50% mortality 2
- Prior chemotherapy: 66.7% mortality 2
- Secondary bacteremia with identified source: 11.1% mortality 2
Critical Pitfalls to Avoid
- Never use aminoglycosides as monotherapy - intrinsic high-level resistance via efflux pump mechanism 3
- Avoid third-generation cephalosporins (ceftriaxone, cefotaxime) - intrinsically resistant 1
- Do not delay catheter removal in persistent bacteremia despite appropriate antibiotics 2, 1
- Recognize multiply resistant strains - verify susceptibilities as resistance patterns can vary 4, 1