Overexpression of SmeDEF Efflux Pump Decreases Aminoglycoside Resistance in Stenotrophomonas maltophilia.

The SmeDEF pump of Stenotrophomonas maltophilia is negatively regulated by SmeT. In this study, strains KJΔT (smeT deletion mutant) and KJT-Dm (mutant with a defective SmeT-binding site) showed increased resistance to chloramphenicol/nalidixic acid/macrolides and susceptibility to aminoglycoside. Overexpression of the SmeDEF pump, in either KJΔT or KJT-Dm, downregulated smeYZ expression, which is responsible for the reduced aminoglycoside resistance. Furthermore, the SmeRySy two-component regulatory system was downregulated in response to SmeDEF overexpression, which supports its involvement in the regulatory circuit.