Efflux-related resistance to norfloxacin, dyes, and biocides in bloodstream isolates of Staphylococcus aureus.
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.
DeMarco
Carmen E
CE
Department of Medicine, Division of Infectious Diseases, Wayne State University School of Medicine, Detroit, MI 48201, USA.
Cushing
Laurel A
LA
Frempong-Manso
Emmanuel
E
Seo
Susan M
SM
Jaravaza
Tinevimbo A A
TA
Kaatz
Glenn W
GW
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
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