Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an aerobic, nonfermentative, Gram-negative bacterium which cause uncommon but difficult to treat infections in humans. 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 are slighlty smaller (0.7-1.8 x 0.4-0.7 μm) than other members of the genus. They are motile due to polar flagella and grow well on MacConkey agar producing pigmented colonies. S. maltophilia are catalase positive, oxidase negative (which distinguishes them from most other members of the genus) and have a positive reaction for extracellular DNase.

S. maltophilia is ubiquitous in aqueous environments, soil and plants, including water, urine, or respiratory secretions; it has also been used in biotechnology applications. In immunocompromised patients, S. maltophilia can lead to nosocomial infections.

Pathogenesis
S. maltophila 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 (plastic or metal), and the most effective treatment is removal of the prosthetic material (usually a central venous catheter or similar device). 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 (e.g., blood), then it usually represents true infection.

In immunocompetent individuals, S. maltophila 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.

S. maltophilia is naturally resistant to many broad-spectrum antibiotics (including all carbapenems) and is thus often difficult to eradicate. Many strains of S. maltophilia are sensitive to co-trimoxazole and ticarcillin, though resistance has been increasing. It is not usually sensitive to piperacillin, and sensitivity to ceftazidime is variable.