Identification and detection of Stenotrophomonas maltophilia by rRNA-directed PCR

Stenotrophomonas maltophilia has recently emerged as an important nosocomia l pathogen in immunocompromised patients, in transplant recipients, and in persons with cystic fibrosis (CF). While this organism is nonpathogenic in healthy individuals, it is increasingly associated with morbidity and morta lity in susceptible populations. Recent studies have indicated that for app roximately 10% of CF patients with moderate lung disease, S. maltophilia ca n be cultured from respiratory tract secretions. Identification of S. malto philia can be problematic, and analysis of isolates from the Burkholderia c epacia Research Laboratory and Repository showed that several isolates pres umptively identified as B. cepacia by clinical microbiology laboratories we re in fact S. maltophilia. To overcome the problems associated with definit ive identification, we developed species-specific PCR (SS-PCR) primers, des ignated SM1 and SM4, directed to the 23S rRNA gene, and tested their utilit y to accurately identify S. maltophilia directly from sputum. The SS-PCR wa s developed and tested against a panel of 112 S. maltophilia isolates colle cted from diverse geographic locations. To test for specificity, 43 isolate s from 17 different species were analyzed. PCR with the SM1-SM4 primer pair and isolated genomic DNA as a template resulted in amplification of a band from all S. maltophilia isolates and was uniformly negative for all other species tested, yielding a sensitivity and a specificity of 100% for the SS -PCR. The utility of the SS-PCR to directly identify S. maltophilia in sput um was examined. Thirteen expectorated sputum samples from CF patients were analyzed by SS-PCR Three samples were PCR positive, in complete concordanc e with the conventional laboratory culture. Thus, we have developed an SS-P CR protocol that can rapidly and accurately identify S. maltophilia isolate s and which can be used for the direct detection of this organism in CF pat ient sputum.