Overview of Stenotrophomonas maltophiliaStenotrophomonas maltophilia is an aerobic, Gram-negative, non-fermentative bacillus that is an emerging opportunistic nosocomial pathogen. It commonly causes infections such as bacteremia, pneumonia, and urinary tract infections, particularly in immunocompromised patients, those with prolonged hospitalization, or prior broad-spectrum antibiotic exposure. The organism is intrinsically multidrug-resistant due to mechanisms like beta-lactamase production, efflux pumps, and outer membrane modifications, limiting treatment options.General Antibiotic Susceptibility PatternsSusceptibility varies by geographic region, hospital setting, and isolate, but patterns from recent global studies (2005–2024) show consistent trends. Trimethoprim-sulfamethoxazole (TMP-SMX) remains the first-line therapy, though resistance is rising (up to 10–15% in some areas). Alternative agents include levofloxacin and minocycline, with tigecycline as a salvage option. The organism is typically resistant to most beta-lactams (e.g., carbapenems, penicillins), aminoglycosides, and polymyxins.Susceptibility testing should follow CLSI guidelines, using broth microdilution for accuracy, as commercial automated systems may yield errors (e.g., >10% for levofloxacin). Always perform testing on clinical isolates, as acquired resistance can emerge rapidly during therapy.Summary of Susceptibility RatesThe table below summarizes approximate susceptibility rates (%) from meta-analyses, surveillance programs (e.g., ATLAS, SENTRY), and regional studies (e.g., Korea, Oman, Mayo Clinic, China; data aggregated from 2004–2024). Rates reflect clinical isolates; "High" indicates >90%, "Moderate" 70–90%, "Low" <70%. Variability exists—e.g., TMP-SMX resistance is higher in Asia (up to 15%) than in the US/Europe (<5%).

Antibiotic Class / Agent

Approximate Susceptibility Rate

Notes / MIC Breakpoints (CLSI)

Trimethoprim-Sulfamethoxazole (TMP-SMX)

High (85–95%)

First-line; resistance via sul genes rising globally. MIC ≤2/38 µg/mL (S).

Fluoroquinolones

- Levofloxacin

Moderate (80–92%)

Alternative to TMP-SMX; higher resistance in ICU settings. MIC ≤2 µg/mL (S).

Tetracyclines

- Minocycline

High (95–97%)

Excellent activity; preferred alternative. MIC ≤8 µg/mL (S).

Glycylcyclines

- Tigecycline

Moderate (60–80%)

Salvage option; limited data, variable MICs. MIC ≤2 µg/mL (S).

Cephalosporins

- Ceftazidime

Low–Moderate (50–70%)

Limited use; high error rates in testing. MIC ≤16 µg/mL (S).

Beta-Lactams / Beta-Lactamase Inhibitors

- Ticarcillin-Clavulanate

Moderate (70–85%)

Variable; not first-line due to intrinsic resistance. MIC ≤64/2 µg/mL (S).

Other (e.g., Chloramphenicol)

Moderate (60–80%)

Rarely used; MIC ≤16 µg/mL (S).

Intrinsic Resistance

- Carbapenems (e.g., Meropenem)

0–5%

Avoid; L1/L2 beta-lactamases.

- Aminoglycosides (e.g., Gentamicin)

0–10%

Efflux-mediated; avoid.

- Polymyxins (e.g., Colistin)

0–20%

Temperature-dependent; poor activity.

Treatment Recommendations

  • Monotherapy: TMP-SMX (8–15 mg/kg/day IV/PO TMP component, divided q6–8h) or levofloxacin (750 mg IV/PO daily) for susceptible isolates.

  • Alternatives: Minocycline (100 mg IV/PO q12h) if TMP-SMX intolerant.

  • Combination Therapy: Consider for severe infections (e.g., bacteremia) or resistance—e.g., TMP-SMX + levofloxacin or + tigecycline—though evidence is limited.

  • Duration: 7–14 days, guided by source control (e.g., catheter removal).

  • Prognosis: Mortality 16–61% for bacteremia; worse in ICU, neutropenia, or lack of source control.

Consult local antibiograms and infectious disease specialists, as resistance trends evolve. For specific isolates, perform MIC testing.