Global emergence of trimethoprim/sulfamethoxazole resistance in Stenotrophomonas maltophilia mediated by acquisition of sul genes.

Trimethoprim/sulfamethoxazole (TMP/SMX) resistance remains a serious threat in the treatment of Stenotrophomonas maltophilia infections. We analyzed an international collection of 55 S. maltophilia TMP/SMX-sensitive (S) (n=30) and -resistant (R) (n=25) strains for integrons; sul1, sul2 and dhfr genes; and insertion element common region (ISCR) elements. sul1, as part of a class 1 integron, was detected in 17 of 25 TMP/SMX-R. Nine TMP/SMX-R strains carried sul2; 7 were on large plasmids. Five TMP/SMX-R isolates were positive for ISCR2, and 4 were linked to sul2; 2 others possessed ISCR3. Two ISCR2s were adjacent to floR. Six TMP/SMX-S isolates harbored novel ISCR elements, ISCR9 and ISCR10. Linkage of ISCR3, ISCR9, and ISCR10 to sul2 and dhfr genes was not demonstrated. The data from this study indicate that class 1 integrons and ISCR elements linked to sul2 genes can mediate TMP/SMX resistance in S. maltophilia and are geographically widespread, findings that reinforce the need for ongoing resistance surveillance.