title: Mutations That Enhance the Ciprofloxacin Resistance of Escherichia coli with qnrA1.
abstract: Plasmid-mediated qnr genes provide only a modest decrease in quinolone susceptibility but facilitate the selection of higher-level resistance. In Escherichia coli strain J53 without qnr, ciprofloxacin resistance often involves mutations in the GyrA subunit of DNA gyrase. Mutations in gyrA were absent, however, when 43 mutants with decreased ciprofloxacin susceptibility were selected from J53(pMG252) with qnrA1. Instead, in 13 mutants, individual and whole-genome sequencing identified mutations in marR and soxR associated with increased expression of marA and soxS and, through them, increased expression of the AcrAB pump, which effluxes quinolones. Nine mutants had increased expression of the MdtE efflux pump, and six demonstrated increased expression of the ydhE pump gene. Many efflux mutants also had increased resistance to novobiocin, another pump substrate, but other mutants were novobiocin hypersusceptible. Mutations in rfaD and rfaE in the pathway for inner core lipopolysaccharide (LPS) biosynthesis were identified in five such strains. Many of the pump and LPS mutants had decreased expression of OmpF, the major porin channel for ciprofloxacin entry. Three mutants had increased expression of qnrA that persisted when pMG252 from these strains was outcrossed. gyrA mutations were also rare when mutants with decreased ciprofloxacin susceptibility were selected from E. coli J53 with aac(6')-Ib-cr or qepA. We suggest that multiple genes conferring low-level resistance contribute to enhanced ciprofloxacin resistance selected from an E. coli strain carrying qnrA1, aac(6')-Ib-cr, or qepA because these determinants decrease the effective ciprofloxacin concentration and allow more common but lower-resistance mutations than those in gyrA to predominate.
authors.affiliation: Lahey Hospital and Medical Center, Burlington, Massachusetts, USA Massachusetts General Hospital, Boston, Massachusetts, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: Vinué
authors.affiliation: Lahey Hospital and Medical Center, Burlington, Massachusetts, USA.
authors.forename: Marian A
authors.initials: MA
authors.lastname: Corcoran
authors.affiliation: Massachusetts General Hospital, Boston, Massachusetts, USA.
authors.forename: David C
authors.initials: DC
authors.lastname: Hooper
authors.affiliation: Lahey Hospital and Medical Center, Burlington, Massachusetts, USA gajacoby50@gmail.com.
authors.forename: George A
authors.initials: GA
authors.lastname: Jacoby
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D002939:Ciprofloxacin / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics*; D004927:Escherichia coli Infections / Q000188:drug therapy; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics*; D008070:Lipopolysaccharides / Q000096:biosynthesis / Q000235:genetics; D008074:Lipoproteins / Q000096:biosynthesis; D008565:Membrane Proteins / Q000096:biosynthesis; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000096:biosynthesis; D009675:Novobiocin / Q000494:pharmacology*; D018272:Porins / Q000096:biosynthesis; D012097:Repressor Proteins / Q000235:genetics; D015534:Trans-Activators / Q000096:biosynthesis; D014157:Transcription Factors / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002939:Ciprofloxacin; D027081:DNA Gyrase; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D008070:Lipopolysaccharides; D008074:Lipoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009675:Novobiocin; D018272:Porins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C083497:AcrA protein, E coli; C083496:AcrB protein, E coli; C080002:MarA protein, E coli; C080004:MarR protein, E coli; C477834:MdtE protein, E coli; C109237:OmpF protein; C485384:Qnr protein, E coli; C070724:SoxR protein, Bacteria; C070725:SoxS protein, E coli