title: Efflux-related resistance to norfloxacin, dyes, and biocides in bloodstream isolates of Staphylococcus aureus.
abstract: Efflux is an important resistance mechanism in Staphylococcus aureus, but its frequency in patients with bacteremia is unknown. Nonreplicate bloodstream isolates were collected over an 8-month period, and MICs of four common efflux pump substrates, with and without the broad-spectrum efflux pump inhibitor reserpine, were determined (n = 232). A reserpine-associated fourfold decrease in MIC was considered indicative of efflux. Strains exhibiting efflux of at least two of the four substrates were identified ("effluxing strains" [n = 114]). For these strains, MICs with or without reserpine for an array of typical substrates and the expression of mepA, mdeA, norA, norB, norC, and qacA/B were determined using quantitative real-time reverse transcription-PCR (qRT-PCR). A fourfold or greater increase in gene expression was considered significant. The most commonly effluxed substrates were ethidium bromide and chlorhexidine (100 and 96% of effluxing strains, respectively). qRT-PCR identified strains overexpressing mepA (5 [4.4%]), mdeA (13 [11.4%]), norA (26 [22.8%]), norB (29 [25.4%]), and norC (19 [16.7%]); 23 strains overexpressed two or more genes. Mutations probably associated with increased gene expression included a MepR-inactivating substitution and norA promoter region insertions or deletions. Mutations possibly associated with increased expression of the other analyzed genes were also observed. Effluxing strains comprised 49% of all strains studied (114/232 strains), with nearly half of these overexpressing genes encoding MepA, MdeA, and/or NorABC (54/114 strains). Reduced susceptibility to biocides may contribute to persistence on environmental surfaces, and efflux of drugs such as fluoroquinolones may predispose strains to high-level target-based resistance.
authors.affiliation: Department of Medicine, Division of Infectious Diseases, Wayne State University School of Medicine, Detroit, MI 48201, USA.
authors.forename: Carmen E
authors.initials: CE
authors.lastname: DeMarco
authors.forename: Laurel A
authors.initials: LA
authors.lastname: Cushing
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Frempong-Manso
authors.forename: Susan M
authors.initials: SM
authors.lastname: Seo
authors.forename: Tinevimbo A A
authors.initials: TA
authors.lastname: Jaravaza
authors.forename: Glenn W
authors.initials: GW
authors.lastname: Kaatz
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D004396:Coloring Agents / Q000494:pharmacology*; D003470:Culture Media; D004202:Disinfectants / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000187:drug effects / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D007202:Indicators and Reagents; D008826:Microbial Sensitivity Tests; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics; D009643:Norfloxacin / Q000494:pharmacology*; D010957:Plasmids / Q000235:genetics; D012329:RNA, Bacterial / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013203:Staphylococcal Infections / Q000097:blood / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004396:Coloring Agents; D003470:Culture Media; D004202:Disinfectants; D007202:Indicators and Reagents; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009643:Norfloxacin; D012329:RNA, Bacterial; D001616:beta-Galactosidase; C075040:NorA protein, Staphylococcus