832. Risk Factors for Efflux Pump Overexpression in Fluoroquinolone-Resistant Escherichia coli
Session: Poster Abstract Session: Antimicrobial Resistance: Clinical and Basic Studies
Friday, October 19, 2012
Room: SDCC Poster Hall F-H
  • OST.pdf (231.9 kB)
  • Background: The prevalence of fluoroquinolone resistance in Escherichia coli has markedly increased in recent years. Efflux pump overexpression is an important mechanism of fluoroquinolone resistance in E. coli and has been associated with high rates of resistance to other antimicrobial classes. The objective of this study was to determine risk factors for efflux overexpression among patients with fluoroquinolone-resistant E. coli (FQREC) gastrointestinal tract colonization.

    Methods: This 3-year case-control study was conducted in the University of Pennsylvania Health System. Three annual fecal surveillance surveys were performed hospital-wide, with all patients colonized with FQREC (levofloxacin minimum inhibitory concentration ³8 mcg/mL) eligible for inclusion. Cases and controls were defined on the basis of overexpression of the AcrAB drug efflux pump, as measured indirectly by the organic solvent tolerance (OST) assay. Case patients were designated as those OST-positive, and control patients as those OST-negative. A multivariable logistic regression model was developed to identify risk factors for OST-positivity in patients with FQREC gastrointestinal tract colonization.

    Results: A total of 89 patients were colonized with FQREC over the study period: 44 (49.4%) and 45 (50.6%) patients had isolates that were OST-positive and OST-negative, respectively. On multivariable analyses, location on the surgical service was significantly associated with recovery of OST-positive isolates (odds ratio [OR], 7.36; 95% confidence interval [CI], 1.82-29.7; P=0.005). In addition, patients who had received a first-generation cephalosporin in the 30 days prior to sampling were less likely to have recovery of an OST-positive isolate (OR, 0.20; 95% CI, 0.04-0.94; P=0.04). Nineteen isolates demonstrated clonal relatedness by pulsed field gel electrophoresis, and of these, the majority were OST-negative versus OST-positive (16 and 3 isolates, respectively, P=0.001).

    Conclusion: The clinical and molecular epidemiology of fluoroquinolone resistance is complex, and future studies will need to focus on elucidating the relationship between specific antimicrobial use and resulting selection pressure for various resistance mechanisms.


    Jennifer Han, MD1, Irving Nachamkin, DrPH, MPH2, Pam Tolomeo, MPH3, Xiangqun Mao, PhD2, Warren Bilker, PhD3,4, Ebbing Lautenbach, MD, MPH, MScE1,3,4 and the CDC Prevention Epicenter Program, (1)Division of Infectious Diseases, Dept. of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, (2)Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, (3)Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, PA, (4)Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, PA


    J. Han, None

    I. Nachamkin, None

    P. Tolomeo, None

    X. Mao, None

    W. Bilker, None

    E. Lautenbach, AstraZeneca: Grant Investigator, Research grant
    Cubist: Grant Investigator, Research grant
    3M: Grant Investigator, Research grant
    Merck: Grant Investigator, Research grant

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