What is Stenotrophomonas maltophilia?

What is Stenotrophomonas maltophilia?

Stenotrophomonas maltophilia is a Gram-negative, biofilm-forming bacterium that functions as an emerging multidrug-resistant opportunistic pathogen causing nosocomial infections primarily in immunocompromised patients, with intrinsic resistance to multiple antibiotics including carbapenems. 1, 2, 3

Microbiological Characteristics

• S. maltophilia is a ubiquitous, Gram-negative bacillus found widely in environmental sources, particularly water 1, 4
• The organism forms biofilms on medical devices and surfaces, which contributes significantly to its pathogenicity and persistence in healthcare settings 2, 5
• It exhibits low outer membrane permeability and possesses two chromosomally encoded β-lactamases that contribute to its intrinsic antibiotic resistance 5

Clinical Significance and Epidemiology

• S. maltophilia causes a range of infections including bloodstream infections, pneumonia, respiratory tract infections, urinary tract infections, and skin/soft tissue infections 1, 4, 3
• The prevalence has increased from 0.8-1.4% during 1997-2003 to 1.3-1.68% during 2007-2012 in the general population 2
• Infections are typically nosocomial and transmitted through water sources and contaminated medical equipment 4, 5

High-Risk Populations

The following patient populations are at elevated risk for S. maltophilia infection:

• Immunocompromised hosts, particularly those with underlying malignancy 1, 2
• Patients with cystic fibrosis 2
• Those receiving corticosteroid or immunosuppressant therapy 2
• Patients with indwelling central venous catheters 2
• Individuals exposed to broad-spectrum antibiotics 2
• Patients with chronic lymphocytic leukemia or aplastic anemia 4

However, prevalence is increasing in immunocompetent populations as well 4

Antibiotic Resistance Profile

• S. maltophilia exhibits intrinsic resistance to carbapenems, making it distinct from many other Gram-negative pathogens 3, 5
• Resistance mechanisms include β-lactamase production, expression of Qnr genes, class 1 integrons, and multidrug-resistance efflux pumps 2, 5
• The organism can acquire new resistance through mutation and horizontal gene transfer 5
• Alarming trends show increasing resistance to historically effective agents including ceftazidime, ticarcillin-clavulanate, and fluoroquinolones 2

Clinical Challenge: Colonization vs. Infection

• S. maltophilia is frequently isolated from respiratory secretions as an opportunistic colonizer during broad-spectrum antibiotic treatment rather than as a true pathogen causing pneumonia 6
• Standardized indications to distinguish colonization from true infection are lacking, making clinical assessment challenging 3
• This distinction is critical because treatment decisions should be based on whether the organism is causing disease versus merely colonizing surfaces 3

Epidemiological Importance in Healthcare Settings

• The European Society of Clinical Microbiology and Infectious Diseases emphasizes that S. maltophilia is important epidemiologically, and prevention of spread is critical for control in hospital settings 7
• The organism colonizes medical devices including urinary catheters, endoscopes, and ventilators 5
• Environmental persistence on surfaces (mattresses, beds, bedside tables, washbasins, window sills) facilitates transmission 7

Morbidity and Mortality

• High morbidity and mortality are associated with S. maltophilia infections, particularly in immunocompromised hosts 4
• In neutropenic patients with documented infection, prompt antimicrobial therapy is crucial to avoid fatal outcomes 6
• The severity of illness is increasing, particularly with opportunistic bloodstream infections and pneumonia syndromes 1