title: Virulence characteristics and phylogenetic background of multidrug-resistant and antimicrobial-susceptible clinical isolates of Escherichia coli from across the United States, 2000-2001.
abstract: BACKGROUND
  Increases in antimicrobial resistance in Escherichia coli have been paralleled by an increasing incidence of E. coli sepsis, suggesting a possible link between resistance and virulence.
  
  
  METHODS
  All 76 multidrug-resistant (MDR) E. coli isolates (i.e., those resistant to > or =3 antimicrobial agents, including ampicillin, ceftazidime, trimethoprim-sulfamethoxazole, gentamicin, and ciprofloxacin) reported to the Tracking Resistance in the United States Today studies during 2000-2001 and 76 closely matched pansusceptible control isolates were studied. Extended virulence profiles and E. coli phylogenetic group (A, B1, B2, or D) were compared between groups.
  
  
  RESULTS
  The MDR isolates, which represented predominantly non-B2 phylogenetic groups (91%), exhibited significantly reduced molecular virulence, compared with the predominantly group B2-derived control isolates (58%). Only 30% of MDR isolates, compared with 61% of control isolates (P<.001), qualified as extraintestinal pathogenic E. coli (ExPEC), and even these isolates exhibited significantly lower virulence scores than did susceptible ExPEC (7.25 vs. 9.0; P=.001). Phylogenetic differences accounted for the apparent virulence differences between MDR and control isolates.
  
  
  CONCLUSIONS
  These findings argue against a direct link between virulence traits and antimicrobial resistance in E. coli. Instead, they call into question why non-B2 strains are more commonly MDR, with differential exposure to selection pressure (including in agriculture) as one possible explanation.
authors.affiliation: Mucosal and Vaccine Research Center, Veterans Affairs Medical Center, and Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55417, USA. johns007@umn.edu
authors.forename: James R
authors.initials: JR
authors.lastname: Johnson
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kuskowski
authors.forename: Abby
authors.initials: A
authors.lastname: Gajewski
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Sahm
authors.forename: James A
authors.initials: JA
authors.lastname: Karlowsky
mesh_terms: D018830:Adhesins, Escherichia coli / Q000235:genetics; D016667:Bacterial Capsules / Q000235:genetics; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000145:classification / Q000187:drug effects / Q000235:genetics* / Q000472:pathogenicity*; D004927:Escherichia coli Infections / Q000382:microbiology*; D029968:Escherichia coli Proteins / Q000235:genetics; D036781:Fimbriae Proteins / Q000235:genetics; D006460:Hemolysin Proteins; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics; D008826:Microbial Sensitivity Tests; D015999:Multivariate Analysis; D016133:Polymerase Chain Reaction; D014481:United States; D014774:Virulence; D037521:Virulence Factors / Q000032:analysis* / Q000235:genetics
chemical_list: D018830:Adhesins, Escherichia coli; D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D006460:Hemolysin Proteins; C065231:HlyD protein, E coli; D026901:Membrane Transport Proteins; D037521:Virulence Factors; C034506:aerobactin receptor; C058769:fimH protein, E coli; D036781:Fimbriae Proteins