Comprehensive analysis of resistance-nodulation-cell division superfamily (RND) efflux pumps from Serratia marcescens, Db10

We investigated the role of the resistance-nodulation-cell division superfamily (RND) efflux system on intrinsic multidrug resistance in Serratia marcescens . We identified eight putative RND efflux system genes in the S . marcescens Db10 genome that included the previously characterized systems, sdeXY , sdeAB , and sdeCDE . Six out of the eight genes conferred multidrug resistance on KAM32, a drug hypersensitive strain of Escherichia coli . Five out of the eight genes conferred resistance to benzalkonium, suggesting the importance of RND efflux systems in biocide resistance in S . marcescens . The energy-dependent efflux activities of five of the pumps were examined using a rhodamine 6 G efflux assay. When expressed in the tolC -deficient strain of E . coli , KAM43, none of the genes conferred resistance on E . coli . When hasF , encoding the S . marcescens TolC ortholog, was expressed in KAM43, all of the genes conferred resistance on E . coli , suggesting that HasF is a major outer membrane protein that is used by all RND efflux systems in this organism. We constructed a sdeXY deletion mutant from a derivative strain of the clinically isolated multidrug-resistant S . marcescens strain and found that the sdeXY deletion mutant was sensitive to a broad spectrum of antimicrobial agents.