Virulence Characteristics and Phylogenetic Background of Multidrug-Resistant and Antimicrobial-Susceptible Clinical Isolates of Escherichia Coli From Across the United States, 2000-2001

J Infect Dis. 2004 Nov 15;190(10):1739-44. doi: 10.1086/425018. Epub 2004 Oct 7.


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.

MeSH terms

  • Adhesins, Escherichia coli / genetics
  • Bacterial Capsules / genetics
  • Bacterial Outer Membrane Proteins / genetics
  • DNA, Bacterial / genetics
  • Drug Resistance, Multiple, Bacterial*
  • Escherichia coli / classification
  • Escherichia coli / drug effects
  • Escherichia coli / genetics*
  • Escherichia coli / pathogenicity*
  • Escherichia coli Infections / microbiology*
  • Escherichia coli Proteins / genetics
  • Fimbriae Proteins / genetics
  • Hemolysin Proteins
  • Humans
  • Membrane Transport Proteins / genetics
  • Microbial Sensitivity Tests
  • Multivariate Analysis
  • Polymerase Chain Reaction
  • United States
  • Virulence
  • Virulence Factors / analysis*
  • Virulence Factors / genetics


  • Adhesins, Escherichia coli
  • Bacterial Outer Membrane Proteins
  • DNA, Bacterial
  • Escherichia coli Proteins
  • Hemolysin Proteins
  • HlyD protein, E coli
  • Membrane Transport Proteins
  • Virulence Factors
  • aerobactin receptor
  • fimH protein, E coli
  • Fimbriae Proteins