Stenotrophomonas maltophilia Infection
S. maltophilia is the only member of the genus Stenotrophomonas, and was originally classed with the Pseudomonads. It is a nonsporulating aerobic gram-negative rod, found in a wide variety of environments and geographical regions. Nosocomial sources most often include wet areas, such as shower heads and faucets, but also blood-sampling tubes, central venous pressure monitors, dialysis machines and inhalation therapy equipment. The organism is frequently present as a colonizer, but may cause true infection. Risk factors for acquisition include chronic lung disease, neoplastic lesions, cystic fibrosis, mechanical ventilation and hospitalization in an intensive care unit.
The most common site of S. maltophilia in hospitalized patients is the respiratory tract, accounting for 56-69% of isolates, although the majority of patients are colonized rather than infected at this site. S. maltophilia is reported to cause 5% of nosocomial pneumonias, which are associated with mechanical ventilation, tracheostomy, previous exposure to broad-spectrum antibiotics, and the use of respiratory therapy equipment such as nebulizers. Many patients also have preexisting lung conditions such as chronic obstructive pulmonary disease, bronchiectasis, kyphoscoliosis, or endobronchial obstruction. True respiratory tract infection with S. maltophilia is associated with significantly increased mortality.
Bacteremia is a common manifestation of S. maltophilia infection, and appears to be increasing frequency.Bacteremia may be secondary to a pulmonary, urinary or gastrointestinal source, although often the initial site of infection is not apparent. S. Maltophilia septicemia may be complicated by disseminated intravascular coagulation (DIC), purpura fulminans and ecthyma gangrenosum. There have been several reports of S. maltophilia endocarditis, with most cases occurring in IV drug abusers or as a complication of prosthetic valve surgery. Other reported sites of S. maltophilia infection include urinary tract, skin and soft tissue, bone and joint, central nervous system, and ocular including corneal ulcers in contact lens users.
Infections caused by S. maltophilia are particularly difficult to manage because of resistance to many antimicrobial agents, including imipenem, most other B-lactams, and aminoglycosides. Variable activity has been reported with fluoroquinolones, tetracyclines, ticarcillin/clavulanate, and trimethoprim/ sulfamethoxazole. Methodological problems associated with susceptibility testing limit the ability to predict susceptibility and ultimate therapeutic efficacy.
According to the National Committee for Clinical Laboratory Standards (NCCLS), routine susceptibility testing on this isolate should not be performed.
