Stenotrophomonas maltophilia is NOT susceptible to piperacillin-tazobactam (Tazocin)
S. maltophilia should not be treated with piperacillin-tazobactam, as this organism demonstrates intrinsic resistance to this agent and its use may actually select for more resistant strains.
Intrinsic Resistance Profile
S. maltophilia is uniformly resistant to carbapenems due to a ubiquitous metallo-β-lactamase, and demonstrates poor susceptibility to most β-lactam antibiotics including piperacillin-tazobactam 1
In vitro susceptibility testing shows 0% of S. maltophilia isolates are susceptible to piperacillin-tazobactam using broth microdilution methods 2
The organism's β-lactamases hydrolyze piperacillin even in the presence of tazobactam, rendering the combination ineffective 3
Previous treatment with piperacillin-tazobactam is actually a risk factor for subsequent isolation of levofloxacin-resistant S. maltophilia, suggesting this agent selects for more resistant strains 4
Susceptibility Testing Pitfalls
Disk diffusion and E-test methods show poor agreement with reference methods for piperacillin-tazobactam against S. maltophilia, with kappa values <0.4 indicating unreliable results 5
The Phoenix automated system also demonstrates poor correlation for piperacillin-tazobactam susceptibility testing in S. maltophilia 5
Significant discrepancies exist between different testing methods for β-lactam-β-lactamase inhibitor combinations, making interpretation unreliable 6
Recommended Treatment Options
First-line therapy:
- High-dose trimethoprim-sulfamethoxazole (TMP-SMX) at 15-20 mg/kg/day of the trimethoprim component is the definitive first-line treatment with strong evidence 7, 8
Alternative options:
- Tigecycline (100 mg IV loading dose, then 50 mg IV every 12 hours) shows 83.8% susceptibility 7
- Minocycline is a non-inferior alternative to TMP-SMX 7
- Levofloxacin or ticarcillin-clavulanate may be used only if documented susceptibility is confirmed 1, 8
Clinical Context
S. maltophilia is more frequently an opportunistic colonizer rather than a true pathogen, particularly in patients receiving broad-spectrum antibiotics 1, 8
True infection should be distinguished from colonization based on clinical indicators including new infiltrates, fever, increased oxygen requirements, and rising inflammatory markers 8
Treatment duration should be at least 14 days in immunocompromised patients 7, 8
For catheter-related bloodstream infections, catheter removal should be strongly considered in addition to antimicrobial therapy 8