Class 1 integrons increase trimethoprim-sulfamethoxazole MICs against epidemiologically unrelated Stenotrophomonas maltophilia isolates

Abstract

Twenty-five plasmid-specified antimicrobial resistance determinants common to gram-negative bacilli from nosocomial infection were investigated from 31 Stenotrophomonas maltophilia isolates. Twenty-four clones were identified by pulsed-field gel electrophoresis, and in three clones that exhibited an increased trimethoprim-sulfamethoxazole MIC, the sul1 determinant was found. These results support not only the higher spread of class 1 integrons compared to other mechanisms but also the potential limitation of using trimethoprim-sulfamethoxazole for therapy of severe S. maltophilia infections.

FIG. 1.

(A) SpeI macrorestriction clustering analysis of S. maltophilia isolate fingerprints. The cutoff level for clones was 75% of similarity. The R1 isolate showed a banding pattern similarity of 95% to another isolate of the same cluster and was classified as a subtype. (B) Macrorestriction fingerprint of nine S. maltophilia isolates digested with SpeI. Lane 1, isolate 13 (clone S); lane 2, isolate 1 (clone A); Lane 3, isolate 3 (clone B); lane 4, isolate 4 (clone C); lane 5, isolate 11 (clone R); lane 6, isolate 6 (clone D); lane 7, isolate 7 (clone E); lane 8, isolate 8 (clone F); lane 9, isolate 9 (clone G); lane 10, isolate 10 (clone H); M, lambda phage ladder DNA concatemers (band sizes are expressed on the right in kilobases).

FIG. 2.

Class 1 integrons found in S. maltophilia strains. Isolates 3 and 11 harbored new cassette rearrangements. Isolate 13 harbored a cassette order described previously.