SmeOP-TolCSm Efflux Pump Contributes to the Multidrug Resistance of Stenotrophomonas maltophilia

A five-gene cluster, tolC Sm -pcm-smeRo-smeO-smeP , of Stenotrophomonas maltophilia was characterized. The presence of smeOP and smeRo-pcm-tolC Sm operons was verified by reverse transcription (RT)-PCR. Both operons were negatively regulated by the TetR-type transcriptional regulator SmeRo, as demonstrated by quantitative RT-PCR and a promoter-fusion assay. SmeO and SmeP were associated with TolC Sm (the TolC protein of S. maltophilia ) for the assembly of a resistance-nodulation-cell-division (RND)-type pump. The compounds extruded by SmeOP-TolC Sm mainly included nalidixic acid, doxycycline, amikacin, gentamicin, erythromycin, leucomycin, carbonyl cyanide 3-chlorophenylhydrazone, crystal violet, sodium dodecyl sulfate, and tetrachlorosalicylanilide.