What is Stenotrophomonas maltophilia?

Stenotrophomonas maltophilia: An Opportunistic Multidrug-Resistant Pathogen

Stenotrophomonas maltophilia is a gram-negative, non-fermenting bacillus that has emerged as an important opportunistic nosocomial pathogen, particularly in immunocompromised patients, characterized by intrinsic multidrug resistance and causing infections with significant morbidity and mortality. 1

Microbiology and Epidemiology

• Originally classified as Pseudomonas maltophilia, later Xanthomonas maltophilia, before receiving its current classification
• Ubiquitous organism found in water sources, soil, and plants
• Increasingly recognized in healthcare settings, particularly on medical devices and equipment 2
• Intrinsically resistant to many antibiotics due to:
  • Low outer membrane permeability
  • Multidrug-resistance efflux systems
  • Two chromosomally encoded β-lactamases
  • Intrinsic resistance to carbapenems due to metallo-β-lactamase 1

Clinical Presentations

S. maltophilia can cause various infections, most commonly:

• Respiratory tract infections: Particularly pneumonia in ventilated patients
• Bloodstream infections: Often associated with indwelling catheters
• Skin and soft tissue infections (SSTIs):
  • Can present as cellulitis, abscesses, or ecthyma gangrenosum
  • Ecthyma gangrenosum appears as painless erythematous papules that rapidly become painful and necrotic within 24 hours 3
• Urinary tract infections: Often associated with urinary catheters

Risk Factors

• Immunocompromised status: Particularly neutropenia 3
• Prolonged hospitalization
• Prior broad-spectrum antibiotic therapy
• Mechanical ventilation
• Indwelling medical devices: Catheters, endoscopes, ventilators 2
• Hematologic malignancies

Diagnosis

• Culture and identification from clinical specimens
• Molecular methods for rapid identification
• Antimicrobial susceptibility testing is essential but challenging due to:
  • Molecular heterogeneity among strains
  • Uneven distribution of resistance determinants
  • Lack of standardized breakpoints for many antibiotics 4

Treatment

First-Line Therapy:

• High-dose trimethoprim-sulfamethoxazole (TMP-SMX): 15-20 mg/kg/day of the trimethoprim component for 7-14 days 1

Alternative Options (when TMP-SMX cannot be used):

• Minocycline: Comparable efficacy to TMP-SMX, particularly useful in patients with acute kidney injury 1
• Fluoroquinolones: Based on susceptibility testing
• Tigecycline: Shows favorable in vitro activity against S. maltophilia 1

For Severe Infections:

• Consider combination therapy for severe infections 1
• Duration of treatment for most bacterial SSTIs should be 7-14 days 3

Infection Control Measures

Based on ESCMID guidelines for managing multidrug-resistant gram-negative bacteria 3:

• Hand hygiene: Strong recommendation with moderate evidence

  • Implement hand hygiene education programs
  • Use alcohol-based hand rub before and after patient contact
  • Soap and water when hands are visibly soiled

• Contact precautions: Conditional recommendation with moderate evidence

  • Gloves and gowns for all colonized patient encounters
  • Prompt removal after care followed by hand hygiene
  • Regular audit of adherence

• Environmental cleaning: Conditional recommendation with moderate evidence

  • Monitor cleaning performance
  • Review disinfectant agents and methods
  • Consider environmental sampling from surfaces in contact with colonized patients

• Education: Conditional recommendation with moderate evidence

  • Ensure healthcare workers understand the epidemiological importance of S. maltophilia
  • Regular multidisciplinary meetings to implement interventions

Special Considerations

• In neutropenic patients, S. maltophilia can cause ecthyma gangrenosum, a cutaneous vasculitis that may be rapidly progressive 3
• Surgical intervention is recommended for drainage of soft tissue abscesses after marrow recovery 3
• Colony-stimulating factor therapy or granulocyte transfusions are not routinely recommended for neutropenic patients with S. maltophilia infections 3

Prognosis

• Infections can be associated with significant mortality, particularly in immunocompromised hosts
• Early appropriate antimicrobial therapy is crucial for improved outcomes
• Regular monitoring of clinical response is essential, with consideration of alternative therapy if no improvement after 7 days 1