title: Characterization of small-colony-variant Stenotrophomonas maltophilia isolated from the sputum specimens of five patients with cystic fibrosis.
abstract: Cystic fibrosis (CF) patients are predisposed to chronic respiratory infection by nonfermentative gram-negative bacilli, including Stenotrophomonas maltophilia. S. maltophilia is highly resistant to most antibiotics, with the exception of sulfamethoxazole-trimethoprim (SXT). SXT-resistant S. maltophilia has been reported, but the mechanism of resistance is not well defined. Repeated findings of suspected small-colony-variant (SCV) S. maltophilia isolates from the sputa of five CF patients were confirmed by partial 16S rRNA gene sequencing. The SCV S. maltophilia isolates were the only S. maltophilia isolates in these cultures, and none were clonally related. DNA fingerprint analysis confirmed that once established, the SCV S. maltophilia strains persisted. Nutritional studies of SCV S. maltophilia have suggested auxotrophy in hemin, methionine, and thymidine associated with resistance to multiple antibiotics, including SXT. The phenotypic switch from wild-type to SCV S. maltophilia was reproducible in vitro by exposure to SXT, suggesting that prolonged exposure to antibiotics may select for both the SCV S. maltophilia phenotype and SXT resistance by interference with the dihydrofolate reductase pathway. Recovery of SCV S. maltophilia from the sputum of CF patients has implications for both laboratory testing and patient management.
authors.affiliation: Department of Laboratories and Pathology, Children's Hospital and Regional Medical Center, University of Washington School of Medicine, Seattle, WA 98105, USA.
authors.forename: Scott W
authors.initials: SW
authors.lastname: Anderson
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Stapp
authors.forename: Jane L
authors.initials: JL
authors.lastname: Burns
authors.forename: Xuan
authors.initials: X
authors.lastname: Qin
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D003470:Culture Media; D003550:Cystic Fibrosis / Q000382:microbiology*; D016172:DNA Fingerprinting / Q000379:methods; D004269:DNA, Bacterial / Q000032:analysis; D016521:Electrophoresis, Gel, Pulsed-Field; D005838:Genotype; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D016133:Polymerase Chain Reaction / Q000379:methods; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013183:Sputum / Q000382:microbiology*; D020615:Stenotrophomonas maltophilia / Q000145:classification* / Q000187:drug effects / Q000254:growth & development* / Q000302:isolation & purification; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D015662:Trimethoprim, Sulfamethoxazole Drug Combination