Ann Lab Med.  2015 Mar;35(2):246-249. 10.3343/alm.2015.35.2.246.

The sul1 Gene in Stenotrophomonas maltophilia With High-Level Resistance to Trimethoprim/Sulfamethoxazole

  • 1Department of Laboratory Medicine, Ewha Womans University School of Medicine, Seoul, Korea.
  • 2Department of Laboratory Medicine, CHA Bundang Medical Center, CHA University, Seongnam, Korea.
  • 3Department of Laboratory Medicine, Yonsei University College of Medicine, Seoul, Korea.
  • 4Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Seoul, Korea.


Emerging resistance to trimethoprim/sulfamethoxazole (SXT) poses a serious threat to the treatment of Stenotrophomonas maltophilia infections. We determined the prevalence and molecular characteristics of acquired SXT resistance in recent clinical S. maltophilia isolates obtained from Korea. A total of 252 clinical isolates of S. maltophilia were collected from 10 university hospitals in Korea between 2009 and 2010. Antimicrobial susceptibility was determined by using the CLSI agar dilution method. The sul1, sul2, and sul3 genes, integrons, insertion sequence common region (ISCR) elements, and dfrA genes were detected using PCR. The presence of the sul1 gene and integrons was confirmed through sequence analysis. Among the 32 SXT-resistant isolates, sul1 was detected in 23 isolates (72%), all of which demonstrated high-level resistance (> or =64 mg/L) to SXT. The sul1 gene (varying in size and structure) was linked to class 1 integrons in 15 of the 23 isolates (65%) harboring this gene. None of the SXT-susceptible isolates or the SXT-resistant isolates with a minimum inhibitory concentration of 4 and 8 mg/L were positive for sul1. Moreover, the sul2, sul3, and dfrA genes or the ISCR elements were not detected. The sul1 gene may play an important role in the high-level SXT resistance observed in S. maltophilia.


Stenotrophomonas maltophilia; Trimethoprim/sulfamethoxazole; sul; Class 1 integron

MeSH Terms

Anti-Bacterial Agents/pharmacology
Bacterial Proteins/*genetics
Drug Resistance, Bacterial/genetics
Gram-Negative Bacterial Infections/microbiology/pathology
Microbial Sensitivity Tests
Stenotrophomonas maltophilia/*drug effects/genetics/isolation & purification
Trimethoprim, Sulfamethoxazole Drug Combination/*pharmacology
Anti-Bacterial Agents
Bacterial Proteins
Trimethoprim, Sulfamethoxazole Drug Combination
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