title: Mutation in the sdeS gene promotes expression of the sdeAB efflux pump genes and multidrug resistance in Serratia marcescens.
abstract: Serratia marcescens gained resistance to both biocides and antibiotics on expressing the SdeAB efflux pump, following exposure to increasingly higher concentrations of a biocide (H. Maseda et al., Antimicrob. Agents Chemother. 53:5230-5235, 2009). To reveal the regulatory mechanism of sdeAB expression, wild-type cells were subjected to transposon-mediated random mutagenesis, and a mutant with antibiotic resistance, which mimicked the phenotype of the previous biocide-resistant cells, was obtained. The transposon element was found in the chromosomal DNA downstream of the sdeAB operon. Sequencing revealed the presence of an open reading frame (ORF) encoding a protein with 159 amino acid residues that is highly similar to the BadM-type transcriptional repressor, designated sdeS. The level of sdeB::xylE reporter gene expression, undetectable in the wild-type cells, appeared to be fully comparable to that in the biocide-resistant cells. Nucleotide sequencing of the mutant revealed sdeS to have a single G-to-A base substitution at position 269 that converted Trp90 to a stop codon. Introduction of a plasmid-borne intact sdeS into the mutant cells and the biocide-resistant cells resulted in a reduction in sdeB::xylE reporter activity to an undetectable level. These results suggested that SdeS functions as a repressor of the sdeAB operon. It was concluded that the original biocide-resistant cells had an impaired sdeS and, therefore, a derepressed level of the SdeAB efflux pump.
authors.affiliation: Institute of Technology and Science, The University of Tokushima Graduate School, 2-1 Minamijosanjima-cho, Tokushima 770-8506, Japan. maseda@bio.tokushima-u.ac.jp
authors.forename: Hideaki
authors.initials: H
authors.lastname: Maseda
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Hashida
authors.forename: Akihiro
authors.initials: A
authors.lastname: Shirai
authors.forename: Takeshi
authors.initials: T
authors.lastname: Omasa
authors.forename: Taiji
authors.initials: T
authors.lastname: Nakae
mesh_terms: D004202:Disinfectants / Q000494:pharmacology; D024901:Drug Resistance, Multiple, Bacterial; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D009643:Norfloxacin / Q000493:pharmacokinetics; D009876:Operon; D012706:Serratia marcescens / Q000187:drug effects* / Q000235:genetics*
chemical_list: D004202:Disinfectants; D009643:Norfloxacin