Nature Publishing Group Acta Medica Okayama 2045-2322 9 2019 Comprehensive analysis of resistance-nodulation-cell division superfamily (RND) efflux pumps from Serratia marcescens, Db10 4854 EN Shinsuke Toba Department of Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Yusuke Minato Department of Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Yuma Kondo Department of Microbiology, Institute of Biomedical & Health Sciences, Hiroshima University Kanami Hoshikawa Department of Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Shu Minagawa Shiho Komaki Department of Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Takanori Kumagai Department of Microbiology, Institute of Biomedical & Health Sciences, Hiroshima University Yasuyuki Matoba Department of Microbiology, Institute of Biomedical & Health Sciences, Hiroshima University Daichi Morita Department of Microbiology, Institute of Biomedical & Health Sciences, Hiroshima University Wakano Ogawa Department of Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Naomasa Gotoh Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University Tomofusa Tsuchiya Department of Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University Teruo Kuroda Department of Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University 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 coil. 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 6G efflux assay. When expressed in the toiC-deficient strain of E. coil, KAM43, none of the genes conferred resistance on E. coil. When hasF, encoding the S. marcescens ToIC ortholog, was expressed in KAM43, all of the genes conferred resistance on E. coil, 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. No potential conflict of interest relevant to this article was reported.