Stenotrophomonas Maltophilia

Updated: Sep 16, 2021
  • Author: Sara Ahmed, MBBS, FCPS, MRCP(UK); Chief Editor: Michael Stuart Bronze, MD  more...
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Stenotrophomonas maltophilia previously known as (Xanthomonas) maltophilia is an aerobic gram-negative bacillus that is found in various aquatic environments. Although an uncommon pathogen in humans, S maltophilia infection in humans, especially nosocomial, has been increasingly recognized.

S maltophilia is an organism of low virulence and frequently colonizes fluids used in the hospital setting (eg, hospital tap water, [1]  irrigation solutions, intravenous fluids) and patient secretions (eg, respiratory secretions, urine, wound exudates). S maltophilia usually must bypass normal host defenses to cause human infection. For example, if an irrigation solution becomes colonized with this organism, irrigating an open wound can cause colonization or infection of the wound. S maltophilia is usually incapable of causing disease in healthy hosts without the assistance of invasive medical devices that bypass normal host defenses. [2]

Risk factors associated with S maltophilia infection have been defined and may include underlying malignancy, immunosuppressant therapy, cystic  fibrosis, COPD, HIV, neutropenia, mechanical ventilation, prior colonization with stenotrophomonas, central venous catheter, genitourinary catheter, continuous ambulatory peritoneal dialysis (CAPD), recent surgery, trauma, prolonged hospitalization, ICU admission, and exposure to broad-spectrum antibiotics, third or fourth generation cephalosporins and carbapenems, and hyperalimentation. [3, 4, 5, 6, 7]





S maltophilia has few pathogenic mechanisms and, for this reason, predominantly results in colonization rather than infection. The main virulence factors that lend to disease pathogenesis include production of a variety of extracellular enzymes, evasion of host immune response, and triggering intense tissue inflammation.

If infection does occur, invasive medical devices are usually the vehicles through which the organism bypasses normal host defenses. Bacterial factors that contribute toward colonization of respiratory tract or prosthetic devices such as intravascular, surgical catheters and endotracheal tubes include cationic surface charge, flagella and fimbriae, which assist adhesion, and biofilm formation.




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S maltophilia is a noninvasive organism that has low virulence. It frequently colonizes body fluids but rarely causes infection (eg, intravenous line infections).


S maltophilia frequently colonizes the respiratory tract in patients with cystic fibrosis. [8, 9, 10, 11, 12]

The 2016 Cystic Fibrosis Foundation Patient Registry Annual Data Report shows a 13% prevalence of S maltophilia; this figure changed little over the preceding decade. [13]


Mortality and morbidity relate to the inoculum of S maltophilia that is able to bypass normal host defense mechanisms.

If an intravenous infusion contains large numbers of S maltophilia, then direct injection into the bloodstream may result in the signs and symptoms associated with gram-negative bacteremia.

Similarly, in the urinary tract, if urological irrigation fluids that contain large numbers of S maltophilia are used during an invasive urological procedure, eg, cystoscopy, then gram-negative bacteremia may occur with its attendant mortality and morbidity, which depend on host factors.

S maltophilia bacteremia is associated with high morbidity and mortality rates and should be considered in patients with recent use of broad-spectrum antibiotics or recent isolation from any other site. The 30-day all-cause mortality rate associated with S maltophilia bacteremia (33.3%) is reported to be more than that of bacteremia caused by Pseudomonas aeruginosa (21.5%; P  =  0.080) and Acinetobacter species (17.3%; P  =  0.041). The independent factor associated with 30-day mortality was the SOFA score. [14]




The course S maltophilia infection depends on the site of the infection, severity, response to antibiotics, and existence of other comorbidities. S maltophilia infections may be life-threatening, especially in immunocompromised patients. [15]