title: Phenotypic and genotypic characterization of fecal Escherichia coli isolates with decreased susceptibility to fluoroquinolones: results from a large hospital-based surveillance initiative.
abstract: BACKGROUND
  The prevalence of fecal colonization with Escherichia coli that has reduced susceptibility to fluoroquinolones is unknown. A detailed characterization of such isolates is limited.
  
  
  METHODS
  We conducted 3 annual fecal surveillance initiatives at 2 hospitals from 2002 to 2004. All E. coli isolates with reduced susceptibility to fluoroquinolones (minimum inhibitory concentration [MIC] to levofloxacin, > or = 0.125 microg/mL) were identified. We characterized gyrA and parC mutations and organic solvent tolerance (OST). Isolates were compared using pulsed-field gel electrophoresis.
  
  
  RESULTS
  Of 789 fecal samples, 149 (18.9%) revealed E. coli with reduced susceptibility to fluoroquinolones. Of 149 isolates, 102 (68.5%) had a MIC > or = 8 microg/mL, 138 (92.6%) had > or = 1 gyrA mutation, 101 (67.8%) had > or = 1 parC mutation, and 59 (39.6%) demonstrated OST. Isolates with a MIC > or = 8 versus <8 microg/mL had more target mutations (median, 3 vs. 1; P<.001) and more often exhibited OST (51% vs. 15%; P<.001). Of 149 isolates, 144 (96.6%) demonstrated a MIC > or = 16 microg/mL to nalidixic acid. The prevalence of OST differed across study years (P = .01). There was no clonal spread of isolates.
  
  
  CONCLUSIONS
  Colonization by E. coli with reduced fluoroquinolone susceptibility is common, and fluoroquinolone-resistance characteristics differ significantly over time. Resistance to nalidixic acid may be useful in the identification of E. coli with early resistance mutations.
authors.affiliation: Division of Infectious Diseases, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6021, USA. elautenb@cceb.med.upenn.edu
authors.forename: Ebbing
authors.initials: E
authors.lastname: Lautenbach
authors.forename: Neil O
authors.initials: NO
authors.lastname: Fishman
authors.forename: Joshua P
authors.initials: JP
authors.lastname: Metlay
authors.forename: Xiangqun
authors.initials: X
authors.lastname: Mao
authors.forename: Warren B
authors.initials: WB
authors.lastname: Bilker
authors.forename: Pam
authors.initials: P
authors.lastname: Tolomeo
authors.forename: Irving
authors.initials: I
authors.lastname: Nachamkin
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics; D027101:DNA Topoisomerase IV / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field / Q000379:methods; D004926:Escherichia coli / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology*; D005243:Feces / Q000382:microbiology*; D024841:Fluoroquinolones / Q000494:pharmacology*; D005838:Genotype; D006761:Hospitals; D006801:Humans; D064704:Levofloxacin; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009268:Nalidixic Acid / Q000494:pharmacology; D015242:Ofloxacin / Q000494:pharmacology; D010641:Phenotype; D011159:Population Surveillance; D012997:Solvents / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D012997:Solvents; D009268:Nalidixic Acid; D064704:Levofloxacin; D015242:Ofloxacin; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase