Stenotrophomonas maltophilia is an aerobic, nonfermentative, Gram-negative bacterium.
It is an uncommon bacterium and human infection is difficult to treat.
Initially classified as Pseudomonas maltophilia, S. maltophilia was also grouped in the genus
Xanthomonas before eventually becoming the type species of the genus Stenotrophomonas
in 1993.
S. maltophilia is slightly smaller than other members of the genus.
They are motile due to polar flagella, and grow well on MacConkey agar producing pigmented
colonies.
S. maltophilia is catalase-positive, oxidase-negative and has a positive reaction for extracellular
DNase.
S. maltophilia is ubiquitous in aqueous environments, soil, and plants; it has also been used in
biotechnology applications.
In immunocompromised patients, S. maltophilia can lead to nosocomial infections.
Pathogenesis S. maltophilia frequently colonizes breathing
tubes such as endotracheal or tracheostomy tubes, the respiratory tract and indwelling
urinary catheters.
Infection is usually facilitated by the presence of prosthetic material, and the most effective
treatment is removal of the prosthetic material.
The growth of S. maltophilia in microbiological cultures of respiratory or urinary specimens
is therefore sometimes difficult to interpret and not a proof of infection.
If, however, it is grown from sites which would be normally sterile, then it usually
represents true infection.
In immunocompetent individuals, S. maltophilia is a relatively unusual cause of pneumonia,
urinary tract infection, or blood stream infection; in immunocompromised patients, however, S.
maltophilia is a growing source of latent pulmonary infections.
S. maltophilia colonization rates in individuals with cystic fibrosis have been increasing.
Treatment S. maltophilia is naturally resistant to many
broad-spectrum antibiotics due to the production of two inducible chromosomal metallo-β-lactamases.
This makes treatment of infected patients very difficult.
S. maltophilia is ubiquitously present in the environment and impossible to eradicate,
which makes prevention also extremely difficult.
Sensitivity testing requires nonstandard culture techniques.
Testing at the wrong temperature results in isolates being incorrectly reported as being
susceptible when they are in fact resistant.
Disc diffusion methods should not be used, as they are unreliable, and agar dilution
should be used instead.
S. maltophilia is not a virulent organism and removal of the infected prosthesis is
frequently sufficient to cure the infection; antibiotics are only required if the prosthesis
cannot be removed.
Many strains of S. maltophilia are sensitive to co-trimoxazole and ticarcillin, though
resistance has been increasing.
It is not usually susceptible to piperacillin, and susceptibility to ceftazidime is variable.
Tigecycline is also an effective drug.
Polymyxin B may be effective treatment, at least in vitro, though not without frequent
adverse effects.
Epidemiology Stenotrophomonas infections have been associated
with high morbidity and mortality in severely immunocompromised and debilitated individuals.
Risk factors associated with Stenotrophomonas infection include HIV infection, malignancy,
cystic fibrosis, neutropenia, mechanical ventilation, central venous catheters, recent surgery,
trauma, and broad-spectrum antibiotic use.
References
External links Stenotrophomonas maltophilia article at eMedicine.
The genus Stenotrophomonas Stenotrophomonas Genome Projects from Genomes
OnLine Database [1] Relevance to Cystic Fibrosis
Effect of different antibiotics eg minocycline, Tigecycline; JAC 2002 correspondence