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

Virulence characteristics and phylogenetic background of multidrug-resistant and antimicrobial-susceptible clinical isolates of Escherichia coli from across the United States, 2000-2001.

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  • 1Mucosal and Vaccine Research Center, Veterans Affairs Medical Center, and Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55417, USA. johns007@umn.edu

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.

PMID:
15499527
[PubMed - indexed for MEDLINE]
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