title: Antimicrobial susceptibility and combination testing of invasive Stenotrophomonas maltophilia isolates.
abstract: BACKGROUND
  Treatment of invasive Stenotrophomonas maltophilia infections is difficult due to this organism's inherent multidrug resistance and increasing resistance to trimethoprim-sulfamethoxazole via acquisition of the sul genes.
  
  
  METHODS
  In vitro antibiotic susceptibility testing was performed using a customized broth microdilution panel. Combination testing for tigecycline with anti-Stenotrophomonas agents (i.e. colistin, ticarcillin-clavulanate, ceftazidime, and levofloxacin) was done using the cross Etest method. Genotyping was done using automated repetitive PCR.
  
  
  RESULTS
  A total of 90 patients with invasive S. maltophilia infections included: (79%) adults, and 21% children or infants [6/12 (50%) cases occurred in infants aged ≤ 1 year.]. S. maltophilia isolates were recovered from blood (69%), lower respiratory (21%) or other sites (CSF, peritoneal fluid) (11%). Seventeen percent of the isolates were SXT-R, and also demonstrated multi-drug resistant to two or more antibiotic classes. Minocycline, tigecycline and colistin had the best in vitro activities. The combination testing of tigecycline and colistin gave the best results; 12 isolates were tested and synergy occurred in 3 isolates while an additional 7 isolates showed additive results.
  
  
  CONCLUSIONS
  We recommend further evaluation with killing assays and clinical studies to evaluate the effectiveness of tigecycline and colistin combination for invasive S. maltophilia infections.
authors.affiliation: Division of Microbiology, Calgary Laboratory Services, Calgary, Alberta, Canada.
authors.forename: Deirdre
authors.initials: D
authors.lastname: Church
authors.forename: Tracie
authors.initials: T
authors.lastname: Lloyd
authors.forename: Gisele
authors.initials: G
authors.lastname: Peirano
authors.forename: Johann
authors.initials: J
authors.lastname: Pitout
mesh_terms: D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002648:Child; D015331:Cohort Studies; D024881:Drug Resistance, Bacterial; D005838:Genotype; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006801:Humans; D007223:Infant; D008826:Microbial Sensitivity Tests / Q000379:methods*; D058889:Molecular Typing / Q000379:methods; D016133:Polymerase Chain Reaction; D020615:Stenotrophomonas maltophilia / Q000145:classification / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D015662:Trimethoprim, Sulfamethoxazole Drug Combination