Stenotrophomonas maltophilia is a bacterium commonly found in various environments. While it is widespread in nature, it generally poses no threat to healthy individuals.
The Nature of Stenotrophomonas maltophilia
Stenotrophomonas maltophilia is classified as a Gram-negative bacterium, meaning it has a thin peptidoglycan layer in its cell wall and an outer membrane, which causes it to appear pink or red under a microscope after Gram staining. It is an aerobic bacterium, requiring oxygen for growth, and is also non-fermenting, distinguishing it from other common bacteria like those in the Enterobacterales family. This rod-shaped bacterium is often motile due to the presence of polar flagella, allowing it to move in its environment.
This bacterium is highly adaptable and can survive in nutrient-poor aqueous environments. Its natural habitats include various water sources, soil, and even the rhizosphere of plants. Within healthcare settings, S. maltophilia can colonize hospital tap water, irrigation solutions, intravenous fluids, and patient secretions like respiratory fluids.
When Stenotrophomonas maltophilia Causes Infection
Stenotrophomonas maltophilia is considered an opportunistic pathogen, meaning it primarily causes infections in individuals with weakened immune systems or those with specific underlying health conditions. It has become an increasing concern in healthcare settings. The bacterium’s ability to form biofilms on various surfaces, including medical devices, contributes to its persistence in hospital environments.
Individuals at higher risk for S. maltophilia infections include those who are immunocompromised, such as patients with malignancy, HIV, or those undergoing immunosuppressant therapy. Patients with chronic illnesses like cystic fibrosis or chronic obstructive pulmonary disease (COPD) are also susceptible. Hospitalized patients, especially those on mechanical ventilation or with indwelling medical devices like central venous catheters or urinary catheters, face increased risk. Prior exposure to broad-spectrum antibiotics, particularly carbapenems, can create an ecological niche for S. maltophilia to emerge.
Common infections caused by S. maltophilia include respiratory tract infections, such as pneumonia, particularly ventilator-associated pneumonia (VAP). Bloodstream infections, or bacteremia, are another frequent manifestation. Other types of infections include wound infections, urinary tract infections, and, less commonly, infections of bones, joints, and the eye. S. maltophilia can also be found in polymicrobial infections, often alongside other bacteria like Pseudomonas aeruginosa.
Diagnosing and Treating Stenotrophomonas maltophilia Infections
Diagnosing Stenotrophomonas maltophilia infections involves isolating the bacterium from clinical specimens. This typically begins with culture-based techniques from affected sites such as blood, sputum, urine, or wounds. Once cultured, biochemical tests or molecular methods like Polymerase Chain Reaction (PCR) or sequencing are used for accurate identification. However, distinguishing true infection from mere colonization, especially in respiratory or urinary samples, can be challenging.
S. maltophilia produces two inducible chromosomal metallo-β-lactamases (L1 and L2) which confer broad resistance to many antibiotics, including most beta-lactams, cephalosporins, and carbapenems. This intrinsic resistance significantly limits available treatment options.
Trimethoprim-sulfamethoxazole (TMP/SMX) is often considered the first-line treatment due to its generally good activity against S. maltophilia, with susceptibility rates typically ranging from 79% to 96%. However, resistance to TMP/SMX is increasing in some regions.
Other antibiotics that may be considered include minocycline, often with high susceptibility rates (e.g., over 95%), and fluoroquinolones like levofloxacin, though resistance to these agents can also vary. Ticarcillin/clavulanate is another option, but its effectiveness can be limited, with susceptibility ranging from 18% to 25% in some studies. Newer agents like cefiderocol or a combination of ceftazidime/avibactam with aztreonam are being explored for severe or multidrug-resistant cases.
Infection control measures in healthcare settings are also important to prevent the spread of S. maltophilia. These measures include strict hand hygiene, appropriate use of personal protective equipment, environmental cleaning and disinfection, and proper maintenance of medical devices. Surveillance and monitoring for S. maltophilia colonization and infection within hospitals also contribute to prevention efforts. The duration of treatment varies, with pneumonia cases typically treated for 7-14 days and bacteremia cases for 14 days.